Clear barriers have sprung up at restaurants, nail salons and school classrooms, but most of the time, they do little to stop the spread of the coronavirus.Covid precautions have turned many parts of our world into a giant salad bar, with plastic barriers separating sales clerks from shoppers, dividing customers at nail salons and shielding students from their classmates.Intuition tells us a plastic shield would be protective against germs. But scientists who study aerosols, air flow and ventilation say that much of the time, the barriers don’t help and probably give people a false sense of security. And sometimes the barriers can make things worse.Research suggests that in some instances, a barrier protecting a clerk behind a checkout counter may redirect the germs to another worker or customer. Rows of clear plastic shields, like those you might find in a nail salon or classroom, can also impede normal air flow and ventilation.Under normal conditions in stores, classrooms and offices, exhaled breath particles disperse, carried by air currents and, depending on the ventilation system, are replaced by fresh air roughly every 15 to 30 minutes. But erecting plastic barriers can change air flow in a room, disrupt normal ventilation and create “dead zones,” where viral aerosol particles can build up and become highly concentrated.“If you have a forest of barriers in a classroom, it’s going to interfere with proper ventilation of that room,” said Linsey Marr, professor of civil and environmental engineering at Virginia Tech and one of the world’s leading experts on viral transmission. “Everybody’s aerosols are going to be trapped and stuck there and building up, and they will end up spreading beyond your own desk.”There are some situations in which the clear shields might be protective, but it depends on a number of variables. The barriers can stop big droplets ejected during coughs and sneezes from splattering on others, which is why buffets and salad bars often are equipped with transparent sneeze guards above the food.But Covid-19 spreads largely through unseen aerosol particles. While there isn’t much real-world research on the impact of transparent barriers and the risk of disease, scientists in the United States and Britain have begun to study the issue, and the findings are not reassuring.A study published in June and led by researchers from Johns Hopkins, for example, showed that desk screens in classrooms were associated with an increased risk of coronavirus infection. In a Massachusetts school district, researchers found that plexiglass dividers with side walls in the main office were impeding air flow. A study looking at schools in Georgia found that desk barriers had little effect on the spread of the coronavirus compared with ventilation improvements and masking.Before the pandemic, a study published in 2014 found that office cubicle dividers were among the factors that may have contributed to disease transmission during a tuberculosis outbreak in Australia.British researchers have conducted modeling studies simulating what happens when a person on one side of a barrier — like a customer in a store — exhales particles while speaking or coughing under various ventilation conditions. The screen is more effective when the person coughs, because the larger particles have greater momentum and hit the barrier. But when a person speaks, the screen doesn’t trap the exhaled particles — which just float around it. While the store clerk may avoid an immediate and direct hit, the particles are still in the room, posing a risk to the clerk and others who may inhale the contaminated air.“We have shown this effect of blocking larger particles, but also that the smaller aerosols travel over the screen and become mixed in the room air within about five minutes,” said Catherine Noakes, professor of environmental engineering for buildings at the University of Leeds in England. “This means if people are interacting for more than a few minutes, they would likely be exposed to the virus regardless of the screen.”Dr. Noakes said erecting barriers may seem like a good idea but can have unintended consequences. She conducted a study published in 2013 that looked at the effect of partitions between beds in hospitals. The study showed that while some people were protected from germs, the partitions funneled the air in the room toward others.So while a worker behind a transparent barrier might be spared some of the customer’s germs, a worker nearby or customers in line could still be exposed. Dr. Noakes said most screens she has seen are “poorly positioned and are unlikely to be of much benefit.”“I think this may be a particular problem in places like classrooms where people are present for longer periods of time,” Dr. Noakes said. “Large numbers of individual screens impede the airflow and create pockets of higher and lower risk that are hard to identify.”To understand why screens often have little effect on protecting people from aerosol particles, it helps to think about exhaled breath like a plume of cigarette smoke, Dr. Marr said.“One way to think about plastic barriers is that they are good for blocking things like spitballs but ineffective for things like cigarette smoke,” Dr. Marr said. “The smoke simply drifts around them, so they will give the person on the other side a little more time before being exposed to the smoke. Meanwhile, people on the same side with the smoker will be exposed to more smoke, since the barriers trap it on that side until it has a chance to mix throughout the space.”Most researchers say the screens most likely help in very specific situations. A bus driver, for instance, shielded from the public by a floor-to-ceiling barrier is probably protected from inhaling much of what passengers are exhaling. A bank cashier behind a wall of glass or a clerk checking in patients in a doctor’s office may be at least partly protected by a barrier..css-1xzcza9{list-style-type:disc;padding-inline-start:1em;}.css-3btd0c{font-family:nyt-franklin,helvetica,arial,sans-serif;font-size:1rem;line-height:1.375rem;color:#333;margin-bottom:0.78125rem;}@media (min-width:740px){.css-3btd0c{font-size:1.0625rem;line-height:1.5rem;margin-bottom:0.9375rem;}}.css-3btd0c strong{font-weight:600;}.css-3btd0c em{font-style:italic;}.css-w739ur{margin:0 auto 5px;font-family:nyt-franklin,helvetica,arial,sans-serif;font-weight:700;font-size:1.125rem;line-height:1.3125rem;color:#121212;}#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-family:nyt-cheltenham,georgia,’times new roman’,times,serif;font-weight:700;font-size:1.375rem;line-height:1.625rem;}@media (min-width:740px){#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-size:1.6875rem;line-height:1.875rem;}}@media (min-width:740px){.css-w739ur{font-size:1.25rem;line-height:1.4375rem;}}.css-9s9ecg{margin-bottom:15px;}.css-16ed7iq{width:100%;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;-webkit-box-pack:center;-webkit-justify-content:center;-ms-flex-pack:center;justify-content:center;padding:10px 0;background-color:white;}.css-pmm6ed{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;}.css-pmm6ed > :not(:first-child){margin-left:5px;}.css-5gimkt{font-family:nyt-franklin,helvetica,arial,sans-serif;font-size:0.8125rem;font-weight:700;-webkit-letter-spacing:0.03em;-moz-letter-spacing:0.03em;-ms-letter-spacing:0.03em;letter-spacing:0.03em;text-transform:uppercase;color:#333;}.css-5gimkt:after{content:’Collapse’;}.css-rdoyk0{-webkit-transition:all 0.5s ease;transition:all 0.5s ease;-webkit-transform:rotate(180deg);-ms-transform:rotate(180deg);transform:rotate(180deg);}.css-eb027h{max-height:5000px;-webkit-transition:max-height 0.5s ease;transition:max-height 0.5s ease;}.css-6mllg9{-webkit-transition:all 0.5s ease;transition:all 0.5s ease;position:relative;opacity:0;}.css-6mllg9:before{content:”;background-image:linear-gradient(180deg,transparent,#ffffff);background-image:-webkit-linear-gradient(270deg,rgba(255,255,255,0),#ffffff);height:80px;width:100%;position:absolute;bottom:0px;pointer-events:none;}.css-uf1ume{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-box-pack:justify;-webkit-justify-content:space-between;-ms-flex-pack:justify;justify-content:space-between;}.css-wxi1cx{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;-webkit-align-self:flex-end;-ms-flex-item-align:end;align-self:flex-end;}.css-12vbvwq{background-color:white;border:1px solid #e2e2e2;width:calc(100% – 40px);max-width:600px;margin:1.5rem auto 1.9rem;padding:15px;box-sizing:border-box;}@media (min-width:740px){.css-12vbvwq{padding:20px;width:100%;}}.css-12vbvwq:focus{outline:1px solid #e2e2e2;}#NYT_BELOW_MAIN_CONTENT_REGION .css-12vbvwq{border:none;padding:10px 0 0;border-top:2px solid #121212;}.css-12vbvwq[data-truncated] .css-rdoyk0{-webkit-transform:rotate(0deg);-ms-transform:rotate(0deg);transform:rotate(0deg);}.css-12vbvwq[data-truncated] .css-eb027h{max-height:300px;overflow:hidden;-webkit-transition:none;transition:none;}.css-12vbvwq[data-truncated] .css-5gimkt:after{content:’See more’;}.css-12vbvwq[data-truncated] .css-6mllg9{opacity:1;}.css-qjk116{margin:0 auto;overflow:hidden;}.css-qjk116 strong{font-weight:700;}.css-qjk116 em{font-style:italic;}.css-qjk116 a{color:#326891;-webkit-text-decoration:underline;text-decoration:underline;text-underline-offset:1px;-webkit-text-decoration-thickness:1px;text-decoration-thickness:1px;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:visited{color:#326891;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:hover{-webkit-text-decoration:none;text-decoration:none;}A study by researchers with the National Institute for Occupational Safety and Health in Cincinnati tested different sized transparent barriers in an isolation room using a cough simulator. The study, which hasn’t yet been peer-reviewed, found that under the right conditions, taller shields, above “cough height,” stopped about 70 percent of the particles from reaching the particle counter on the other side, which is where the store or salon worker would be sitting or standing.But the study’s authors noted the limitations of the research, particularly that the experiment was conducted under highly controlled conditions. The experiment took place in an isolation room with consistent ventilation rates that didn’t “accurately reflect all real-world situations,” the report said.The study didn’t consider that workers and customers move around, that other people could be in the room breathing the redirected particles and that many stores and classrooms have several stations with acrylic barriers, not just one, that impede normal air flow.While further research is needed to determine the effect of adding transparent shields around school or office desks, all the aerosol experts interviewed agreed that desk shields were unlikely to help and were likely to interfere with the normal ventilation of the room. Depending on the conditions, the plastic shields could cause viral particles to accumulate in the room.“If there are aerosol particles in the classroom air, those shields around students won’t protect them,” said Richard Corsi, the incoming dean of engineering at the University of California, Davis. “Depending on the air flow conditions in the room, you can get a downdraft into those little spaces that you’re now confined in and cause particles to concentrate in your space.”Aerosol scientists say schools and workplaces should focus on encouraging workers and eligible students to be vaccinated, improving ventilation, adding HEPA air filtering machines when needed and imposing mask requirements — all of which are proven ways to reduce virus transmission.The problem, experts say, is that most people in charge of erecting barriers in offices, restaurants, nail salons and schools are not doing so with the assistance of engineering experts who can evaluate air flow and ventilation for each room.People shouldn’t panic when they see transparent barriers, but they shouldn’t view them as fully protective, either. Workers and students who have transparent shields around them should continue to wear a mask to lower risk, Dr. Corsi said.“Air flow in rooms is pretty complicated,” Dr. Corsi said. “Every room is different in terms of the arrangement of the furniture, the height of the walls and ceilings, the vents, where the book shelves are. All of these things have a huge impact on the actual flow and air distribution in a room because every classroom or office space is different.”

Clear barriers have sprung up at restaurants, nail salons and school classrooms, but most of the time, they do little to stop the spread of the coronavirus.Covid precautions have turned many parts of our world into a giant salad bar, with plastic barriers separating sales clerks from shoppers, dividing customers at nail salons and shielding students from their classmates.Intuition tells us a plastic shield would be protective against germs. But scientists who study aerosols, air flow and ventilation say that much of the time, the barriers don’t help and probably give people a false sense of security. And sometimes the barriers can make things worse.Research suggests that in some instances, a barrier protecting a clerk behind a checkout counter may redirect the germs to another worker or customer. Rows of clear plastic shields, like those you might find in a nail salon or classroom, can also impede normal air flow and ventilation.Under normal conditions in stores, classrooms and offices, exhaled breath particles disperse, carried by air currents and, depending on the ventilation system, are replaced by fresh air roughly every 15 to 30 minutes. But erecting plastic barriers can change air flow in a room, disrupt normal ventilation and create “dead zones,” where viral aerosol particles can build up and become highly concentrated.“If you have a forest of barriers in a classroom, it’s going to interfere with proper ventilation of that room,” said Linsey Marr, professor of civil and environmental engineering at Virginia Tech and one of the world’s leading experts on viral transmission. “Everybody’s aerosols are going to be trapped and stuck there and building up, and they will end up spreading beyond your own desk.”There are some situations in which the clear shields might be protective, but it depends on a number of variables. The barriers can stop big droplets ejected during coughs and sneezes from splattering on others, which is why buffets and salad bars often are equipped with transparent sneeze guards above the food.But Covid-19 spreads largely through unseen aerosol particles. While there isn’t much real-world research on the impact of transparent barriers and the risk of disease, scientists in the United States and Britain have begun to study the issue, and the findings are not reassuring.A study published in June and led by researchers from Johns Hopkins, for example, showed that desk screens in classrooms were associated with an increased risk of coronavirus infection. In a Massachusetts school district, researchers found that plexiglass dividers with side walls in the main office were impeding air flow. A study looking at schools in Georgia found that desk barriers had little effect on the spread of the coronavirus compared with ventilation improvements and masking.Before the pandemic, a study published in 2014 found that office cubicle dividers were among the factors that may have contributed to disease transmission during a tuberculosis outbreak in Australia.British researchers have conducted modeling studies simulating what happens when a person on one side of a barrier — like a customer in a store — exhales particles while speaking or coughing under various ventilation conditions. The screen is more effective when the person coughs, because the larger particles have greater momentum and hit the barrier. But when a person speaks, the screen doesn’t trap the exhaled particles — which just float around it. While the store clerk may avoid an immediate and direct hit, the particles are still in the room, posing a risk to the clerk and others who may inhale the contaminated air.“We have shown this effect of blocking larger particles, but also that the smaller aerosols travel over the screen and become mixed in the room air within about five minutes,” said Catherine Noakes, professor of environmental engineering for buildings at the University of Leeds in England. “This means if people are interacting for more than a few minutes, they would likely be exposed to the virus regardless of the screen.”Dr. Noakes said erecting barriers may seem like a good idea but can have unintended consequences. She conducted a study published in 2013 that looked at the effect of partitions between beds in hospitals. The study showed that while some people were protected from germs, the partitions funneled the air in the room toward others.So while a worker behind a transparent barrier might be spared some of the customer’s germs, a worker nearby or customers in line could still be exposed. Dr. Noakes said most screens she has seen are “poorly positioned and are unlikely to be of much benefit.”“I think this may be a particular problem in places like classrooms where people are present for longer periods of time,” Dr. Noakes said. “Large numbers of individual screens impede the airflow and create pockets of higher and lower risk that are hard to identify.”To understand why screens often have little effect on protecting people from aerosol particles, it helps to think about exhaled breath like a plume of cigarette smoke, Dr. Marr said.“One way to think about plastic barriers is that they are good for blocking things like spitballs but ineffective for things like cigarette smoke,” Dr. Marr said. “The smoke simply drifts around them, so they will give the person on the other side a little more time before being exposed to the smoke. Meanwhile, people on the same side with the smoker will be exposed to more smoke, since the barriers trap it on that side until it has a chance to mix throughout the space.”Most researchers say the screens most likely help in very specific situations. A bus driver, for instance, shielded from the public by a floor-to-ceiling barrier is probably protected from inhaling much of what passengers are exhaling. A bank cashier behind a wall of glass or a clerk checking in patients in a doctor’s office may be at least partly protected by a barrier..css-1xzcza9{list-style-type:disc;padding-inline-start:1em;}.css-3btd0c{font-family:nyt-franklin,helvetica,arial,sans-serif;font-size:1rem;line-height:1.375rem;color:#333;margin-bottom:0.78125rem;}@media (min-width:740px){.css-3btd0c{font-size:1.0625rem;line-height:1.5rem;margin-bottom:0.9375rem;}}.css-3btd0c strong{font-weight:600;}.css-3btd0c em{font-style:italic;}.css-w739ur{margin:0 auto 5px;font-family:nyt-franklin,helvetica,arial,sans-serif;font-weight:700;font-size:1.125rem;line-height:1.3125rem;color:#121212;}#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-family:nyt-cheltenham,georgia,’times new roman’,times,serif;font-weight:700;font-size:1.375rem;line-height:1.625rem;}@media (min-width:740px){#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-size:1.6875rem;line-height:1.875rem;}}@media (min-width:740px){.css-w739ur{font-size:1.25rem;line-height:1.4375rem;}}.css-9s9ecg{margin-bottom:15px;}.css-16ed7iq{width:100%;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;-webkit-box-pack:center;-webkit-justify-content:center;-ms-flex-pack:center;justify-content:center;padding:10px 0;background-color:white;}.css-pmm6ed{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;}.css-pmm6ed > :not(:first-child){margin-left:5px;}.css-5gimkt{font-family:nyt-franklin,helvetica,arial,sans-serif;font-size:0.8125rem;font-weight:700;-webkit-letter-spacing:0.03em;-moz-letter-spacing:0.03em;-ms-letter-spacing:0.03em;letter-spacing:0.03em;text-transform:uppercase;color:#333;}.css-5gimkt:after{content:’Collapse’;}.css-rdoyk0{-webkit-transition:all 0.5s ease;transition:all 0.5s ease;-webkit-transform:rotate(180deg);-ms-transform:rotate(180deg);transform:rotate(180deg);}.css-eb027h{max-height:5000px;-webkit-transition:max-height 0.5s ease;transition:max-height 0.5s ease;}.css-6mllg9{-webkit-transition:all 0.5s ease;transition:all 0.5s ease;position:relative;opacity:0;}.css-6mllg9:before{content:”;background-image:linear-gradient(180deg,transparent,#ffffff);background-image:-webkit-linear-gradient(270deg,rgba(255,255,255,0),#ffffff);height:80px;width:100%;position:absolute;bottom:0px;pointer-events:none;}.css-uf1ume{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-box-pack:justify;-webkit-justify-content:space-between;-ms-flex-pack:justify;justify-content:space-between;}.css-wxi1cx{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;-webkit-align-self:flex-end;-ms-flex-item-align:end;align-self:flex-end;}.css-12vbvwq{background-color:white;border:1px solid #e2e2e2;width:calc(100% – 40px);max-width:600px;margin:1.5rem auto 1.9rem;padding:15px;box-sizing:border-box;}@media (min-width:740px){.css-12vbvwq{padding:20px;width:100%;}}.css-12vbvwq:focus{outline:1px solid #e2e2e2;}#NYT_BELOW_MAIN_CONTENT_REGION .css-12vbvwq{border:none;padding:10px 0 0;border-top:2px solid #121212;}.css-12vbvwq[data-truncated] .css-rdoyk0{-webkit-transform:rotate(0deg);-ms-transform:rotate(0deg);transform:rotate(0deg);}.css-12vbvwq[data-truncated] .css-eb027h{max-height:300px;overflow:hidden;-webkit-transition:none;transition:none;}.css-12vbvwq[data-truncated] .css-5gimkt:after{content:’See more’;}.css-12vbvwq[data-truncated] .css-6mllg9{opacity:1;}.css-qjk116{margin:0 auto;overflow:hidden;}.css-qjk116 strong{font-weight:700;}.css-qjk116 em{font-style:italic;}.css-qjk116 a{color:#326891;-webkit-text-decoration:underline;text-decoration:underline;text-underline-offset:1px;-webkit-text-decoration-thickness:1px;text-decoration-thickness:1px;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:visited{color:#326891;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:hover{-webkit-text-decoration:none;text-decoration:none;}A study by researchers with the National Institute for Occupational Safety and Health in Cincinnati tested different sized transparent barriers in an isolation room using a cough simulator. The study, which hasn’t yet been peer-reviewed, found that under the right conditions, taller shields, above “cough height,” stopped about 70 percent of the particles from reaching the particle counter on the other side, which is where the store or salon worker would be sitting or standing.But the study’s authors noted the limitations of the research, particularly that the experiment was conducted under highly controlled conditions. The experiment took place in an isolation room with consistent ventilation rates that didn’t “accurately reflect all real-world situations,” the report said.The study didn’t consider that workers and customers move around, that other people could be in the room breathing the redirected particles and that many stores and classrooms have several stations with acrylic barriers, not just one, that impede normal air flow.While further research is needed to determine the effect of adding transparent shields around school or office desks, all the aerosol experts interviewed agreed that desk shields were unlikely to help and were likely to interfere with the normal ventilation of the room. Depending on the conditions, the plastic shields could cause viral particles to accumulate in the room.“If there are aerosol particles in the classroom air, those shields around students won’t protect them,” said Richard Corsi, the incoming dean of engineering at the University of California, Davis. “Depending on the air flow conditions in the room, you can get a downdraft into those little spaces that you’re now confined in and cause particles to concentrate in your space.”Aerosol scientists say schools and workplaces should focus on encouraging workers and eligible students to be vaccinated, improving ventilation, adding HEPA air filtering machines when needed and imposing mask requirements — all of which are proven ways to reduce virus transmission.The problem, experts say, is that most people in charge of erecting barriers in offices, restaurants, nail salons and schools are not doing so with the assistance of engineering experts who can evaluate air flow and ventilation for each room.People shouldn’t panic when they see transparent barriers, but they shouldn’t view them as fully protective, either. Workers and students who have transparent shields around them should continue to wear a mask to lower risk, Dr. Corsi said.“Air flow in rooms is pretty complicated,” Dr. Corsi said. “Every room is different in terms of the arrangement of the furniture, the height of the walls and ceilings, the vents, where the book shelves are. All of these things have a huge impact on the actual flow and air distribution in a room because every classroom or office space is different.”

While the vaccines are effective at preventing serious illness and death, the risk of developing post-Covid health problems after a breakthrough infection isn’t known.While some breakthrough cases among those who are fully vaccinated against Covid-19 are inevitable, they are unlikely to result in hospitalization or death. But one important question about breakthrough infection that remains unanswered is: Can the vaccinated develop so-called long Covid?Long Covid refers to a set of symptoms — such as severe fatigue, brain fog, headache, muscle pain and sleep problems — that can persist for weeks or months after the active infection has ended. The syndrome is poorly understood, but studies suggest that between 10 and 30 percent of adults who catch the virus may experience long Covid, including those who experienced only mild illness or no symptoms at all.But the vast majority of data collected about long Covid has been in the unvaccinated population. The risk of developing long Covid for the fully vaccinated who get infected after vaccination hasn’t been studied.While preliminary research suggests that it is, in fact, possible for a breakthrough case to lead to symptoms that can persist for weeks to months, there are still more questions than answers. What percent of breakthrough cases result in lingering symptoms? How many of those people recover? Are the persistent symptoms after breakthrough infection as severe as those that occur in the unvaccinated?“I just don’t think there is enough data,” said Dr. Zijian Chen, medical director at the Center for Post-Covid Care at Mount Sinai Health System in New York. “It’s too early to tell. The population of people getting sick post vaccination isn’t that high right now, and there’s no good tracking mechanism for these patients.”One recent study of Israeli health care workers published in the New England Journal of Medicine offers a glimpse of the risk of long Covid after a breakthrough infection. Among 1,497 fully vaccinated health care workers, 39 of them — about 2.6 percent — developed breakthrough infections. (All of the workers were believed to be infected after contact with an unvaccinated person, and the study was conducted before the Delta variant became dominant.)While most of the breakthrough cases were mild or asymptomatic, seven out of 36 workers tracked at six weeks (19 percent) still had persistent symptoms. These long Covid symptoms included a mix of prolonged loss of smell, persistent cough, fatigue, weakness, labored breathing or muscle pain.But the study’s authors caution against drawing too many conclusions from the research. The sample size — just seven patients — is small. And the research was designed to study antibody levels in the infected, said Dr. Gili Regev-Yochay, director of the infectious disease epidemiology unit at Sheba Medical Center. It was not designed to study the risk of long Covid after a breakthrough infection, “It was not the scope of this paper,” Dr. Regev-Yochay said. “I don’t think we have an answer to that.”Even so, the fact that one in five of the health care workers who had breakthrough infections still had lingering symptoms after six weeks appears to be the first indication from a peer-reviewed study that long Covid is possible after a breakthrough infection.“People have said to me, ‘You’re fully vaccinated. Why are you being so careful?’” said Dr. Robert M. Wachter, professor and chair of the department of medicine at the University California San Francisco. “I’m still in the camp of I don’t want to get Covid. I don’t want to get a breakthrough infection.”Dr. Wachter said that despite the many limitations of the Israeli study, the data offer more evidence that the vaccinated should keep taking reasonable precautions to avoid the virus.“I’m going to take it at face value that one in five people, six weeks after a breakthrough case, continued to feel crummy,” Dr. Wachter said. “That’s enough to make me want to wear two masks when I go into the grocery store, which is not that burdensome anyway.”.css-1xzcza9{list-style-type:disc;padding-inline-start:1em;}.css-3btd0c{font-family:nyt-franklin,helvetica,arial,sans-serif;font-size:1rem;line-height:1.375rem;color:#333;margin-bottom:0.78125rem;}@media (min-width:740px){.css-3btd0c{font-size:1.0625rem;line-height:1.5rem;margin-bottom:0.9375rem;}}.css-3btd0c strong{font-weight:600;}.css-3btd0c em{font-style:italic;}.css-w739ur{margin:0 auto 5px;font-family:nyt-franklin,helvetica,arial,sans-serif;font-weight:700;font-size:1.125rem;line-height:1.3125rem;color:#121212;}#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-family:nyt-cheltenham,georgia,’times new roman’,times,serif;font-weight:700;font-size:1.375rem;line-height:1.625rem;}@media (min-width:740px){#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-size:1.6875rem;line-height:1.875rem;}}@media (min-width:740px){.css-w739ur{font-size:1.25rem;line-height:1.4375rem;}}.css-9s9ecg{margin-bottom:15px;}.css-16ed7iq{width:100%;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;-webkit-box-pack:center;-webkit-justify-content:center;-ms-flex-pack:center;justify-content:center;padding:10px 0;background-color:white;}.css-pmm6ed{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;}.css-pmm6ed > :not(:first-child){margin-left:5px;}.css-5gimkt{font-family:nyt-franklin,helvetica,arial,sans-serif;font-size:0.8125rem;font-weight:700;-webkit-letter-spacing:0.03em;-moz-letter-spacing:0.03em;-ms-letter-spacing:0.03em;letter-spacing:0.03em;text-transform:uppercase;color:#333;}.css-5gimkt:after{content:’Collapse’;}.css-rdoyk0{-webkit-transition:all 0.5s ease;transition:all 0.5s ease;-webkit-transform:rotate(180deg);-ms-transform:rotate(180deg);transform:rotate(180deg);}.css-eb027h{max-height:5000px;-webkit-transition:max-height 0.5s ease;transition:max-height 0.5s ease;}.css-6mllg9{-webkit-transition:all 0.5s ease;transition:all 0.5s ease;position:relative;opacity:0;}.css-6mllg9:before{content:”;background-image:linear-gradient(180deg,transparent,#ffffff);background-image:-webkit-linear-gradient(270deg,rgba(255,255,255,0),#ffffff);height:80px;width:100%;position:absolute;bottom:0px;pointer-events:none;}.css-uf1ume{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-box-pack:justify;-webkit-justify-content:space-between;-ms-flex-pack:justify;justify-content:space-between;}.css-wxi1cx{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;-webkit-align-self:flex-end;-ms-flex-item-align:end;align-self:flex-end;}.css-12vbvwq{background-color:white;border:1px solid #e2e2e2;width:calc(100% – 40px);max-width:600px;margin:1.5rem auto 1.9rem;padding:15px;box-sizing:border-box;}@media (min-width:740px){.css-12vbvwq{padding:20px;width:100%;}}.css-12vbvwq:focus{outline:1px solid #e2e2e2;}#NYT_BELOW_MAIN_CONTENT_REGION .css-12vbvwq{border:none;padding:10px 0 0;border-top:2px solid #121212;}.css-12vbvwq[data-truncated] .css-rdoyk0{-webkit-transform:rotate(0deg);-ms-transform:rotate(0deg);transform:rotate(0deg);}.css-12vbvwq[data-truncated] .css-eb027h{max-height:300px;overflow:hidden;-webkit-transition:none;transition:none;}.css-12vbvwq[data-truncated] .css-5gimkt:after{content:’See more’;}.css-12vbvwq[data-truncated] .css-6mllg9{opacity:1;}.css-qjk116{margin:0 auto;overflow:hidden;}.css-qjk116 strong{font-weight:700;}.css-qjk116 em{font-style:italic;}.css-qjk116 a{color:#326891;-webkit-text-decoration:underline;text-decoration:underline;text-underline-offset:1px;-webkit-text-decoration-thickness:1px;text-decoration-thickness:1px;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:visited{color:#326891;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:hover{-webkit-text-decoration:none;text-decoration:none;}Complicating the study of breakthrough infections is the fact that the U.S. Centers for Disease Control and Prevention only tracks post-vaccination infections that result in hospitalization or death. While the C.D.C. does continue to study breakthrough infections in several large cohorts, the lack of data on all breakthrough cases remains a source of frustration among scientists and patient advocacy groups.“It’s very frustrating not to have data at this point in the pandemic to know what happens to breakthrough cases,” said Akiko Iwasaki, an immunologist at Yale School of Medicine who is conducting studies of long Covid. “If mild breakthrough infection is turning into long Covid, we don’t have a grasp of that number.”Diana Berrent, founder of Survivor Corps, a Facebook group for people affected by Covid-19 that has about 171,000 members, took an informal poll and found 24 people who said they had lingering symptoms after a breakthrough infection. It’s not a scientific sample, and the cases haven’t been validated, but the poll shows the need for more data on breakthrough cases, Ms. Berrent said.“You can’t extrapolate it to the general population, but it’s a very strong signal that the C.D.C. needs to be mandating reporting of every breakthrough case,” Ms. Berrent said. “We can’t know what we’re not counting.”But some experts predict the surge of new cases caused by the spread of the Delta variant will, unfortunately, lead to more breakthrough cases in the coming months. Dr. Chen of Mount Sinai said it will take several months before patients with long Covid from a breakthrough infection are enrolled in studies.“We’re waiting for these patients to show up at our doors,” Dr. Chen said.Despite the lack of data, one thing is clear: Getting vaccinated will reduce the risk of getting infected and getting long Covid, said Athena Akrami, a neuroscientist at University College London who collected and published data from nearly 4,000 long Covid patients after developing long Covid herself after a March 2020 bout with Covid-19“It’s simple math,” said Dr. Akrami. “If you reduce infections, then the likelihood of long Covid will drop automatically.”

The rise of the Delta variant of the coronavirus has raised new questions about how the vaccinated can stay safe and avoid breakthrough infections. We asked the experts for advice.For the vaccinated, it was supposed to be a worry-free, “hot vax” summer of socializing and fun. But the rise of the highly infectious Delta variant has spoiled those plans.While the vaccines remain remarkably protective against Covid-19, especially against serious illness, headlines about breakthrough infections and new recommendations that vaccinated people should sometimes wear masks have left many people confused and worried.While new research shows vaccinated people can become infected and carry high levels of the coronavirus, it’s important to remember that those cases are rare, and it’s primarily the unvaccinated who get infected and spread the virus.“If you’re vaccinated, you’ve done the most important thing for you and your family and friends to keep everyone safe,” Gregg Gonsalves, assistant professor of epidemiology at the Yale School of Public Health, said. “There’s substantially more freedom for people who are vaccinated, but the idea that everything is the same as the summer of 2019 is not the case.”As long as large numbers of people remain unvaccinated, vaccinated people will be exposed to the Delta variant. Parents have the added worry that children under 12 probably won’t be eligible for vaccination until well into the fall. As a result, every vaccinated person should consider a safety checklist to help minimize the risk of becoming infected and spreading the virus to others.Am I sure the people I’m with are vaccinated? Are they symptom-free?What are the vaccination and case count rates in my community?What is my risk, and the risk of those around me, for complications of Covid-19?We asked the experts 10 questions about how vaccinated people should adjust their lives and behaviors during the Delta surge. Here are their answers.New Guidance for the VaccinatedIf I’m vaccinated, why do I need to worry about Delta?What’s the real risk of a breakthrough infection after vaccination?When should I wear a mask?Should I upgrade my mask?What’s the risk of hanging out with my vaccinated friends and family?Can I still dine at restaurants?Is it safe to travel? Should I skip the peanuts and water and keep my mask on?How safe are buses, subways and trains for vaccinated people?Can I hug and visit older relatives? What about unvaccinated children?How do I know if I have the Delta variant?If I’m vaccinated, why do I need to worry about Delta?No vaccine offers 100 percent protection. Think of vaccine antibodies like a sea wall designed to protect a town from a storm surge, says Erin Bromage, a comparative immunologist and biology professor at the University of Massachusetts, Dartmouth. Most of the time, the wall stands up to the pounding waves, but a hurricane might be forceful enough to allow some water to get through. Compared with earlier forms of the virus, Delta is like a viral hurricane; it’s far more infectious and presents a bigger challenge to even a vaccinated immune system.“Vaccinations give you that extra protection you wouldn’t normally have,” Dr. Bromage said. “But when you hit a big challenge, like getting near an unvaccinated person who has a high viral load, that wall is not always going to hold.”The good news is the current crop of vaccines available in the United States are doing a remarkable job of protecting people from serious illness, hospitalization and death. More than 97 percent of those hospitalized with Covid-19 are unvaccinated. And new data from Singapore shows that even when vaccinated patients are hospitalized with Delta breakthrough infections, they are far less likely to need supplemental oxygen, and they clear the virus faster compared with unvaccinated patients.What’s the real risk of a breakthrough infection after vaccination?Breakthrough infections make headlines, but they remain uncommon. Although the Centers for Disease Control and Prevention stopped tracking all breakthrough cases in May, about half of all states report at least some data on breakthrough events. The Kaiser Family Foundation recently analyzed much of the state-reported data and found that breakthrough cases, hospitalizations and deaths are extremely rare events among those who are fully vaccinated against Covid-19. The rate of breakthrough cases reported among those fully vaccinated is “well below 1 percent in all reporting states, ranging from 0.01 percent in Connecticut to 0.29 percent in Alaska,” according to the Kaiser analysis..css-1xzcza9{list-style-type:disc;padding-inline-start:1em;}.css-3btd0c{font-family:nyt-franklin,helvetica,arial,sans-serif;font-size:1rem;line-height:1.375rem;color:#333;margin-bottom:0.78125rem;}@media (min-width:740px){.css-3btd0c{font-size:1.0625rem;line-height:1.5rem;margin-bottom:0.9375rem;}}.css-3btd0c strong{font-weight:600;}.css-3btd0c em{font-style:italic;}.css-w739ur{margin:0 auto 5px;font-family:nyt-franklin,helvetica,arial,sans-serif;font-weight:700;font-size:1.125rem;line-height:1.3125rem;color:#121212;}#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-family:nyt-cheltenham,georgia,’times new roman’,times,serif;font-weight:700;font-size:1.375rem;line-height:1.625rem;}@media (min-width:740px){#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-size:1.6875rem;line-height:1.875rem;}}@media (min-width:740px){.css-w739ur{font-size:1.25rem;line-height:1.4375rem;}}.css-9s9ecg{margin-bottom:15px;}.css-uf1ume{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-box-pack:justify;-webkit-justify-content:space-between;-ms-flex-pack:justify;justify-content:space-between;}.css-wxi1cx{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;-webkit-align-self:flex-end;-ms-flex-item-align:end;align-self:flex-end;}.css-12vbvwq{background-color:white;border:1px solid #e2e2e2;width:calc(100% – 40px);max-width:600px;margin:1.5rem auto 1.9rem;padding:15px;box-sizing:border-box;}@media (min-width:740px){.css-12vbvwq{padding:20px;width:100%;}}.css-12vbvwq:focus{outline:1px solid #e2e2e2;}#NYT_BELOW_MAIN_CONTENT_REGION .css-12vbvwq{border:none;padding:10px 0 0;border-top:2px solid #121212;}.css-12vbvwq[data-truncated] .css-rdoyk0{-webkit-transform:rotate(0deg);-ms-transform:rotate(0deg);transform:rotate(0deg);}.css-12vbvwq[data-truncated] .css-eb027h{max-height:300px;overflow:hidden;-webkit-transition:none;transition:none;}.css-12vbvwq[data-truncated] .css-5gimkt:after{content:’See more’;}.css-12vbvwq[data-truncated] .css-6mllg9{opacity:1;}.css-qjk116{margin:0 auto;overflow:hidden;}.css-qjk116 strong{font-weight:700;}.css-qjk116 em{font-style:italic;}.css-qjk116 a{color:#326891;-webkit-text-decoration:underline;text-decoration:underline;text-underline-offset:1px;-webkit-text-decoration-thickness:1px;text-decoration-thickness:1px;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:visited{color:#326891;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:hover{-webkit-text-decoration:none;text-decoration:none;}But many breakthrough infections are probably never reported because people who are infected don’t have symptoms or have mild symptoms that end before the person even thinks about being tested.“Breakthrough infections are pretty rare, but unless we have a population-based sample we don’t know the level of rarity,” said Dr. Asaf Bitton, executive director of Ariadne Labs at Brigham and Women’s Hospital and the Harvard T.H. Chan School of Public Health in Boston. “A lot of people with mild scratchy throat for a couple days may have had them, but we don’t know. It’s not a failure of the vaccine that we’re having breakthrough cases. It’s been estimated that we’ve staved of 100,000 to 200,000 deaths since the vaccine campaign started.”What is clear is that the risk of a breakthrough infection increases the more opportunities you give Delta to challenge the wall of protection conferred by your vaccine. Big crowded events — like a July 4 celebration in Provincetown, Mass., or the packed Lollapalooza concert in Chicago — pose a much greater risk that a vaccinated person will cross paths with an infected person carrying a high viral load.“The more people you put yourself in contact with, the more risk you have, but it also depends on the local climate of risk,” Dr. Gonsalves said. “Soon we’ll probably see a Lollapalooza outbreak. All these people crushed together is an ideal situation for the spread of Delta.”When should I wear a mask?The C.D.C. has a color-coded map of Covid-19 outbreaks in the United States. Blue and yellow zones show relatively low levels of infections, while orange and red zones indicate areas where cases in the past week were above 50 cases per 100,000 people. The agency advises people to wear masks if they live in an orange or red zone — which now accounts for about 80 percent of the counties in the United States.Infection numbers remain relatively low in much of the Northeast and Upper Midwest, while Delta has caused huge spikes in cases in Missouri, Arkansas, Louisiana and Florida.The problem with the map is that case counts are changing rapidly and may surge in your local community before the map has changed colors. Even if you’re certain you’re living in a highly vaccinated community with very low case counts, it makes sense to consider the case counts and vaccination rates in nearby communities as well, because people — and viruses — cross state and county boundaries all the time.Most experts agree that you don’t need to wear a mask outdoors if you’re not in a crowd and have plenty of distance (at least six feet) from people whose vaccination status isn’t known. It’s still risky to attend a packed outdoor concert, but if you do, wear a mask.“I would still suggest wearing a mask if you are indoors with people whose vaccination status you don’t know, especially if you will be within a few feet of them for any amount of time, or if you will be in the room for a long period of time with those people,” said J. Alex Huffman, an aerosol scientist and associate professor of chemistry and biochemistry at the University of Denver. “I don’t wear a mask indoors in all situations now, because I’m fully vaccinated, but I put my N95 mask on whenever I go into indoor public spaces.”Should I upgrade my mask?You will get the most protection from a high-quality medical mask like an N95 or a KN95, although you want to be sure you have the real thing. A KF94 is a high-quality medical mask made in Korea, where counterfeits are less likely. If you don’t have a medical mask, you still get strong protection from double masking with a simple surgical mask under a cloth mask. A mask with an exhale valve should never be worn, since it allows plumes of viral particles to escape, and counterfeit masks may have faulty valves that let germs in.You may want to pick your mask based on the setting. A cloth mask may be adequate for a quick trip into an empty convenience store in an area with high vaccination rates. But a higher-quality mask makes sense during air travel or in a crowded grocery store, especially in communities where vaccination rates are low and case counts are high. Masks with straps or ties around the back of the head seal more tightly than masks with ear loops.“All the mitigation efforts we used before need to be better to hold off the Delta variant, and this includes masks,” Dr. Huffman said. “I strongly encourage people to upgrade their mask to something with high filter quality and something that fits tightly to their face. The No. 1 factor, in my opinion, is to make sure the mask is sealed well all around the edges — over the nose bridge, by the cheeks and under the chin. So any mask that fits tightly is better than almost any loosefitting mask.”What’s the risk of hanging out with my vaccinated friends and family?Vaccinated people are at very low risk when they spend time, unmasked, with their vaccinated friends and family members. “I don’t think mask-wearing is critical,” Dr. Huffman said. “If you are indoors with a small number of people you know are vaccinated, wearing a mask is low on my list of worries.”But some circumstances might require extra precautions. While it’s unusual for a vaccinated person to spread the virus to another vaccinated person, it’s theoretically possible. A vaccinated friend who is going to crowded bars, packed concerts or traveling to a Covid hot spot is a bigger risk than someone who avoids crowds and spends most of their time with vaccinated people.With the Delta variant spreading, Dr. Bitton suggests an “outdoor first” strategy, particularly for families with unvaccinated children or family members at high risk. If you can take your event outside to a backyard or patio this summer and minimize your time indoors, you lower your risk.Spending time with smaller groups of vaccinated friends has less risk than attending a big party, even if you believe everyone at the party is vaccinated. If you’re indoors, open the windows to improve ventilation. If someone in the group is at very high risk because of age or because they are immunocompromised, it’s reasonable to ask even vaccinated people to be tested before a visit. A simple rapid home test can even be offered to guests to be sure everyone is Covid-free.Can I still dine at restaurants?The answer depends on local conditions, your tolerance for risk and the personal health of those around you. Risk is lowest in communities with high vaccination rates and very low case counts. A restaurant meal in Vermont, where two-thirds of the population is vaccinated, poses less risk than an indoor meal in Alabama or Mississippi, where just one-third of the residents are vaccinated.Parents of unvaccinated children and people with compromised immune systems, who studies show may get less protection from vaccines, may want to order takeout or dine outdoors as an added precaution.Is it safe to travel? Should I skip the peanuts and water and keep my mask on?Airplanes are typically well ventilated and not a major source of outbreaks, but taking precautions is still a good idea. The potential for exposure to an infected person may be even higher in the terminal, sitting in airport restaurants and bars, or going through the security line. In airplanes, air is refreshed roughly every two to three minutes — a higher rate than in grocery stores and other indoor spaces. While airlines still require passengers to wear masks, people are allowed to remove them to drink water or eat.To prevent air from circulating to everyone throughout the cabin, airplane ventilation systems keep airflow contained to a few rows. As a result, an infected passengers poses most risk to those sitting in the seats in the immediate area. Watch this simulation to see what happens when someone sneezes on an airplane.Most experts say that they use a high-quality medical mask, like an N95 or KF94, when they fly. If you don’t have one, double masking is advised. For a vaccinated person, the risk of removing a mask briefly to eat or drink during a flight is low, but it’s better to keep it on as much as possible. The C.D.C. says it’s best for unvaccinated people, including children, to avoid flying.Dr. Bromage said he recently traveled by air and took his mask off briefly to drink a beverage, but kept it on for most of the flight. He said he would be more comfortable removing his mask to eat if he knew the people next to him were vaccinated. He said he would be more concerned if the person next to him didn’t seem to care about Covid precautions or wore the mask under the nose. “If you’ve got a random person next to you, especially a chatty person, I’d keep the mask on,” he said.How safe are buses, subways and trains for vaccinated people?Most buses, trains and subways still require everyone to wear a mask, which lowers risk. While vaccinated people are well protected, the risk of viral exposure increases the longer the ride and the more crowded the train car or bus. For many people, riding public transit is essential for getting to work or school, and wearing a well-fitted medical mask or double mask is recommended. When public transit is optional, the decision about whether to ride should factor in local vaccination rates and whether case counts are rising.Can I hug and visit older relatives? What about unvaccinated children?While it’s generally considered safe for vaccinated people to hug and spend time together unmasked, parents of unvaccinated children have more risks to consider, particularly when visiting older relatives. In communities with low case counts and high vaccination rates, it’s generally considered safe for unvaccinated children from a single household to spend time with vaccinated grandparents. But as the Delta variant spreads and children return to school, the risks of close contact also increase for older or immune-compromised people who are more vulnerable to complications from Covid-19, even if they’re vaccinated.When families plan a visit to a high-risk relative, it’s a good idea to minimize other exposures, avoiding restaurant dining or working out at the gym in the week leading up to the visit. Even though the risk of a vaccinated person spreading Covid-19 remains low, vaccinated grandparents should also reduce their personal exposure when they spend time with unvaccinated children.“I have not been masking up indoors with my octogenarian parents at this point, because I am still very careful in the way I wear masks in public settings,” Dr. Huffman, the aerosol scientist, said. “But if I had more interactions that increased my overall risk of exposure, I would strongly consider masking up when indoors with vulnerable individuals.”Rapid home tests are an added precaution when visiting grandparents or an immune-compromised family member. Take a test a few days before the visit as well as the day of the visit. You can learn more about home testing here.Home tests are “a wonderful option for people with a little more anxiety right now in regards to the virus,” Dr. Bromage said. “What we’re doing is buying those, and each and everyone tests before they come together — literally right before we’re together. When everyone is clear, you can enjoy that time together.”How do I know if I have the Delta variant?If you’re diagnosed with Covid-19, the odds are overwhelming that you have the Delta variant. The C.D.C. now estimates that Delta accounts for more than 82 percent of cases in the United States. That said, standard Covid tests won’t tell you if your infection was caused by the Delta variant or another variant of the virus. While health departments may use genomic sequencing to identify levels of different variants in a community, this information typically isn’t shared with individuals. You still need to isolate and seek medical advice if you have low blood oxygen levels, have trouble breathing or have other worrisome symptoms. You can learn more about when to seek medical advice here.

With daily reports of breakthrough infections and the rise of the Delta variant, vaccinated people may need to take a few more precautions. Here’s what you need to know.As the Delta variant spreads among the unvaccinated, many fully vaccinated people are also beginning to worry. Is it time to mask up again?While there’s no one-size-fits-all answer to the question, most experts agree that masks remain a wise precaution in certain settings for both the vaccinated and unvaccinated. How often you use a mask will depend on your personal health tolerance and risk, the infection and vaccination rates in your community, and who you’re spending time with.The bottom line is this: While being fully vaccinated protects against serious illness and hospitalization from Covid-19, no vaccine offers 100 percent protection. As long as large numbers of people remain unvaccinated and continue to spread coronavirus, vaccinated people will be exposed to the Delta variant, and a small percentage of them will develop so-called breakthrough infections. Here are answers to common questions about how you can protect yourself and lower your risk for a breakthrough infection.When should a vaccinated person wear a mask?To decide whether a mask is needed, first ask yourself these questions.Are the people I’m with also vaccinated?What’s the case rate and vaccination rate in my community?Will I be in a poorly ventilated indoor space, or outside? Will the increased risk of exposure last for a few minutes or for hours?What’s my personal risk (or the risk for those around me) for complications from Covid-19?Experts agree that if everyone you’re with is vaccinated and symptom-free, you don’t need to wear a mask.“I don’t wear a mask hanging out with other vaccinated people,” said Dr. Ashish K. Jha, dean of the Brown University School of Public Health. “I don’t even think about it. I’m going to the office with a bunch of people, and they’re all vaccinated. I’m not worried about it.”But once you start to venture into enclosed public spaces where the chances of your encountering unvaccinated people is greater, a mask is probably a good idea. Being fully vaccinated remains the strongest protection against Covid-19, but risk is cumulative. The more opportunities you give the virus to challenge the antibodies you’ve built up from your vaccine, the higher your risk of coming into contact with a large enough exposure that the virus will break through the protective barrier provided by your immune system. For that reason, the case rate and vaccination rate of your community is one of the most important factors influencing the need for masks. In Vermont, Massachusetts, Connecticut and Rhode Island, for instance, more than 70 percent of adults are fully vaccinated. In Alabama, Mississippi and Arkansas, fewer than 45 percent of adults are vaccinated. In some counties, overall vaccination rates are far lower.“We’re two Covid nations right now,” said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine and co-director of the Center for Vaccine Development at Texas Children’s Hospital. In Harris County, Texas, where Dr. Hotez lives, case counts are rising, up by 114 percent in the past two weeks, and only 44 percent of the community is fully vaccinated. “I’m wearing a mask indoors most of the time,” said Dr. Hotez.Finally, masking is more important in poorly ventilated indoor spaces than outdoors, where risk of infection is extremely low. Dr. Jah notes that he recently dashed into a coffee shop, unmasked, because vaccination rates are high in his area, and he was only there for a few minutes.Your personal risk matters, too. If you are older or immune compromised, your antibody response to the vaccine may not be as strong as the response in a young person. Avoiding crowded spaces and wearing a mask when you’re indoors and don’t know the vaccination status of those around you is a good idea.Use The Times tracker to find the vaccination rates and case rates in your area.Why is the Delta variant prompting experts to rethink mask guidance?When the U.S. Centers for Disease Control and Prevention announced that vaccinated people could stop wearing masks, case counts were dropping, vaccinations were on the rise and the highly-infectious Delta variant had not yet taken hold. Since then, Delta has spread rapidly and now accounts for more than 83 percent of cases in the United States. People infected with the Delta variant are known to shed much higher levels of virus for longer periods of time compared with earlier lineages of the coronavirus. One preliminary study estimated the viral load is 1,000 times greater in people with the Delta variant. These high viral loads give the virus more opportunities to challenge your antibodies and break through your vaccine’s protection.“This is twice as transmissible as the original lineage of Covid,” said Dr. Hotez. “The reproductive number of the virus is around 6,” he said, referring to the number of people a virus carrier is likely to infect. “That means 85 percent of the population needs to be vaccinated. Only a few areas of the country are reaching that.”Is it safe for vaccinated people to go to restaurants, museums, the movies, a wedding or other large gatherings?The answer depends on your personal risk tolerance and the level of vaccinations and Covid-19 cases in your community. The more time you spend with unvaccinated people in enclosed spaces for long periods of time, the higher your risk of crossing paths with the Delta variant, or any other variants that may crop up. Large gatherings, by definition, offer more opportunities to get infected with coronavirus, even if you’re vaccinated. Scientists have documented breakthrough infections at a recent wedding in Oklahoma and July 4 celebrations in Provincetown, Mass. But even with the Delta variant, full vaccination appears to be about 90 percent effective at preventing serious illness and hospitalization from Covid-19. If you are at very high risk for complications from Covid-19, however, you should consider avoiding risky situations and wearing a mask when the vaccination status of those around you is unknown. Healthy vaccinated people who are at low risk of complications have to decide what level of personal risk they are willing to tolerate. Wearing a mask at larger indoor gatherings will lower their risk for infection. If you’re healthy and vaccinated but caring for an aging parent or spending time with others at high risk, you should consider their risk too when deciding whether to attend an event or wear a mask.“If I go into a public area, I’ll generally wear a mask,” said Dr. Hotez. “Up until recently I took my son and his girlfriend out for dinner in a restaurant, and I wouldn’t wear a mask because transmission was way down. Now I’m not so sure. I may readjust my thinking about restaurants while Delta is accelerating.”If breakthrough infections are rare, why do I keep hearing about them?Breakthrough infections get a lot of attention because vaccinated people talk about them on social media. When clusters of breakthrough infections happen, they also are reported in science journals or the media. But it’s important to remember that while breakthrough cases are relatively rare, they can still occur no matter what vaccine you get. “No vaccines are 100 percent effective at preventing illness in vaccinated people,” the C.D.C. states on its website. “There will be a small percentage of fully vaccinated people who still get sick, are hospitalized or die from Covid-19.” A breakthrough case doesn’t mean your vaccine isn’t working. In fact, most cases of breakthrough infections result in no symptoms or only mild illness, which shows the vaccines are working well to prevent serious illness from Covid-19.As of July 12, more than 159 million people in the United States had been fully vaccinated against Covid-19. Of those, just 5,492 had breakthrough cases that resulted in serious illness, including 1,063 who died. That’s less than 0.0007 percent of the vaccinated population. Meanwhile, 99 percent of deaths from Covid-19 are among the unvaccinated.Many infectious disease experts are frustrated that the C.D.C. is only documenting cases in which a vaccinated person with Covid-19 is hospitalized or dies. But many breakthrough infections still are being detected in asymptomatic people who are being tested frequently, like baseball players and Olympic athletes. Many of those people are traveling or spending extended periods of time in close quarters with others. “Sports figures are different,” said Dr. Jha. “Part of the problem is they are also encountering a lot of unvaccinated people, including in their own little circle.”I’m vaccinated. How often should I be tested for Covid-19?If you’re fully vaccinated and you know you’ve been exposed to someone with Covid-19, it’s a good idea to be tested, even if you don’t have symptoms.And if you have cold symptoms or any other signs of infection, experts agree you should be tested. Many vaccinated people who aren’t wearing masks have picked up summer colds that cause runny noses, fever and coughing. But it’s impossible to tell the difference between a summer cold and Covid-19. Anyone with cough or cold symptoms should wear a mask to protect those around them and get tested to rule out Covid-19. It’s a good idea to keep a few home Covid tests on hand as well.“If I woke up one morning and had cold symptoms, I would put on a mask at home, and I would get myself tested,” said Dr. Jha. “I don’t want to cause breakthrough infections for other members of my family, and I don’t want to give it to my 9-year-old kid.”

As pandemic restrictions begin to relax, common viruses that cause drippy noses, stuffy heads and other cold symptoms have roared back to taunt your immune system.Yes, the summer cold and cough season really is worse than usual.“I’ve had bad colds, but I’ve never experienced a virus like this,” said Holly Riddel, 55, an entrepreneur in Redondo Beach, Calif., who has been suffering from congestion, clogged ears and a raspy throat for about two weeks. “I want this gone. I haven’t been able to work out. I’m just not feeling like myself.”Months of pandemic restrictions aimed at Covid-19 had the unintended but welcome effect of stopping flu, cold and other viruses from spreading. But now that masks are off and social gatherings, hugs and handshakes are back, the run-of-the-mill viruses that cause drippy noses, stuffy heads, coughs and sneezes have also returned with a vengeance.“It was a bad chest cold — chest congestion, a rattling cough,” said Laura Wehrman, 52, a wardrobe supervisor for film and television, who caught a weeklong bug after flying to New York from Austin in late June to visit friends. Although she’s fully vaccinated against Covid-19, she took multiple tests to be sure she wasn’t infected. Eventually a doctor confirmed it was a rhinovirus, a common cold virus. She said several of her other friends also have been sick with colds and coughs as well.“I was staying with one of my best friends, and it got tense for a minute because she had started a new job, and she didn’t want to be sick,” said Ms. Wehrman. “I actually went and checked into a hotel for the last two days so I could just cough away by myself.”Infectious disease experts say there are a number of factors fueling this hot, sneezy summer. While pandemic lockdowns protected many people from Covid-19, our immune systems missed the daily workout of being exposed to a multitude of microbes back when we commuted on subways, spent time at the office, gathered with friends and sent children to day care and school.Although your immune system is likely as strong as it always was, if it hasn’t been alerted to a microbial intruder in a while, it may take a bit longer to get revved up when challenged by a pathogen again, experts say. And while some viral exposures in our past have conferred lasting immunity, other illnesses may have given us only transient immunity that waned as we were isolating at home.“Frequent exposure to various pathogens primes or jazzes up the immune system to be ready to respond to that pathogen,” said Dr. Paul Skolnik, an immunovirologist and chair of internal medicine at the Virginia Tech Carilion School of Medicine. “If you’ve not had those exposures, your immune system may be a little slower to respond or doesn’t respond as fully, leading to greater susceptibility to some respiratory infections and sometimes longer or more protracted symptoms.”The U.S. Centers for Disease Control and Prevention says that cases of common respiratory viruses, including respiratory syncytial virus (R.S.V.) and human parainfluenza viruses, which cause typical cold and flu symptoms, are on the rise this summer. The spike in R.S.V., which can be especially risky to the very young and very old, is particularly unusual for this time of year, said a spokeswoman at the C.D.C., which plans to release a report this week about the pandemic’s effect on a variety of respiratory viruses. The surge in R.S.V. was most notable in several southern states, but the virus has begun to crop up all over the country. Its spread has been tracked primarily in young children, some of whom have been hospitalized with severe symptoms.The R.S.V. surge, which has been seen in Europe, South Africa, Australia and New Zealand as well, is likely the result of pandemic lockdowns, which created a much larger population of susceptible young children. A cohort of babies, now toddlers, were largely protected from the virus when few of us were out and about. Since then, a new group of infants has been born — giving the virus the opportunity to infect roughly twice as many vulnerable children and creating more vectors to spread it to older children and adults, who typically have milder symptoms.Sue Huang, director of the World Health Organization’s National Influenza Centre at the Institute of Environmental Science and Research, New Zealand, said the country’s strict restrictions not only stopped Covid-19 but also wiped out R.S.V. and influenza as well, a finding Dr. Huang and colleagues published in the journal Nature in February.But as the country opened its borders to Australia, cases of R.S.V. spiked in a matter of weeks, as the virus preyed on a larger-than-usual group of susceptible children, many of whom were admitted to hospitals.“I haven’t seen anything like this in 20 years of working as a virologist,” said Dr. Huang. “There’s usually a degree of pre-existing immunity due to the previous winter. When you don’t have that kind of protection, it’s a bit like a wildfire. The fire can just continue, and the chain of transmission keeps going.”While doctors may test young children to confirm a case of R.S.V., and many people who have cold symptoms will be tested to rule out Covid-19, most people probably won’t know the specific respiratory virus causing their symptoms, said Dr. Kathyrn M. Edwards, professor of pediatrics at Vanderbilt University Medical Center.“We’re seeing each other again and sharing our viruses, and I think maybe we are all a little more susceptible to viruses we haven’t seen,” said Dr. Edwards. “To know exactly what each person has is hard to say. In adults, the symptoms by and large are the same, and you can’t tell if it’s R.S.V., rhinovirus, parainfluenza or another cold virus.”Satya Dandekar, an expert in viral infections and mucosal immunology, said that while isolation measures didn’t weaken our immune system, other factors, including stress, poor sleep habits and increased alcohol consumption, could play a role in how an individual immune system responds to a respiratory virus.“There is going to be a tremendous variable response in the community for who is going to respond and deal with infections well and who will get sick,” said Dr. Dandekar, chair of the department of medical microbiology and immunology at the University of California-Davis School of Medicine. “When a person gets exposed to a pathogen, there has to be a rapid ramp up of the response from the immune system and immune cells. With stress and other factors, the army of immune cells is a little hampered and slows down and may not be able to react fast enough to attack, giving enough time for the pathogen to get a hold on the host.”Allison Agwu, an infectious disease specialist at Johns Hopkins Children’s Center, said that even though many pandemic restrictions have been loosened, people should be mindful about taking precautions to prevent the spread of all respiratory illnesses.“Do the things we tell fifth graders: Wash your hands, cover your sneeze, get rest, all those things,” said Dr. Agwu. “And do your best to get vaccinated against the things you can. Get your Covid vaccine so you’re less paranoid when you get a cold.”The higher rate of R.S.V. and other respiratory viruses this summer was largely predicted in a paper last winter published in the Proceedings of the National Academy of Sciences. But what’s not clear is when the flu virus will re-emerge and what effect it will have. Rachel Baker, the study’s lead author and an epidemiologist and research scholar at Princeton University, said a potential worry will be if the flu, R.S.V. and Covid-19 all circulate at the same time.“The big puzzle is where is the flu?” said Dr. Baker. “I think it’s a very uncertain flu season. It’s not necessarily going to be worse, but when is it going to come back? And what is it going to look like?”Dr. Baker noted that she is currently struggling with her own summer cold, which she assumes she picked up when she ventured out to a local pub to watch the recent England versus Italy soccer match, which she felt safe doing after being fully vaccinated against Covid-19.“This was a very crowded pub, everyone was shouting at the TV and no one was wearing a mask apart from me,” she said. “I tried to stand near the door for better circulation. A few days later I got the cold. I can’t believe I wrote the paper on this, and I got the summertime cold.”

Although studies of a third dose are underway, experts agree that the vaccines are still working well, even against the Delta variant, and that booster shots are not necessary right now.Covid-19 booster shots are in the news, but chances are that Americans won’t be getting an extra shot in the arm any time soon.A surprise announcement from the vaccine maker Pfizer-BioNTech that it plans to seek authorization for a booster shot in the United States has prompted new worries among the general public about the effectiveness of Covid vaccines against the highly contagious Delta variant. Pfizer said it plans to seek authorization for a booster shot in the coming weeks, citing the possibility that protection against the coronavirus will wane six to 12 months after full immunization with the current two-shot regimen.But Pfizer’s talk of booster shots has been dismissed as premature by some of the world’s leading vaccine experts, who note that all evidence suggests that the Pfizer shots, along with the Moderna and Johnson & Johnson vaccines, continue to provide strong protection against Covid-19. A joint statement by the Centers for Disease Control and Prevention and the Food and Drug Administration offered a quick rebuke to the Pfizer announcement, noting that public health officials, not private pharmaceutical companies, would make the decision about booster shots.“Americans who have been fully vaccinated do not need a booster shot at this time,” the statement said. “We are prepared for booster doses if and when the science demonstrates that they are needed.”Even so, searches on Google for booster shots surged amid continuing worries about the Delta variant and the risk of breakthrough infections among the vaccinated. Adding to the confusion is the news that Israel’s Ministry of Health said on Monday it would begin offering a third dose of the Pfizer vaccine to adults with weakened immune systems, including cancer and organ transplant patients, in the country’s first step toward booster shots for the most vulnerable.So is a booster shot in your future? We talked to leading experts about whether booster shots are imminent and why it may be risky to give extra doses to the fully vaccinated in wealthy countries when many people around the world haven’t gotten their first shots. Here are answers to common questions.Why is Pfizer talking about booster shots?All of the vaccine companies have been studying booster shots for months, just in case they’re needed in the future. But Pfizer’s announcement that it’s ready to seek approval came as a surprise.In a news release, Pfizer-BioNTech cited recent data from Israel’s Ministry of Health announcing that although the vaccine remains about 93 percent effective at preventing serious illness and hospitalization, the vaccine is about 64 percent effective at stopping breakthrough infections, or infections that occur in those who are fully vaccinated, with or without symptoms. That figure is down from about 95 percent in May, before the highly infectious Delta variant became widespread. Experts say the data from Israel hasn’t been peer-reviewed and may be complicated by a number of variables. Other studies from Britain, Scotland and Canada show the Pfizer vaccine is still about 80 percent to 88 percent effective against the Delta variant.But Pfizer said that the findings from Israel were consistent with its own vaccine studies, and that it planned to present its data to federal health officials. A booster given six months after the second dose of the vaccine increases the potency of antibodies against the original coronavirus and the Beta variant, the form first detected in South Africa, by five- to tenfold, the company said, and it believes a vaccine booster would perform similarly against the Delta variant.“We continue to believe that it is likely, based on the totality of the data we have to date, that a third dose may be needed within six to 12 months after full vaccination,” the company said.What do public health experts say about booster shots?Several public health experts have criticized the Pfizer announcement, calling it “opportunistic” and “irresponsible.” Pfizer’s chief scientific officer met with top U.S. scientists on Monday to discuss the research.“Pfizer doesn’t get to decide when we need boosters; the F.D.A., C.D.C. and other regulatory agencies do that,” said Dr. Carlos del Rio, an infectious disease expert at Emory University. “The data needs to be shown publicly in an open, transparent way.”Dr. del Rio noted that even the data from Israel, cited in the company’s news release, shows the vaccine remains highly effective at protecting people from serious illness. Instead of talking about boosters, the focus should be on getting more shots in the arms of the unvaccinated, he said.“If you’ve been vaccinated, you don’t need to worry about boosters,” Dr. del Rio said. “The people who need to worry are those that haven’t been vaccinated. The booster is to get more people vaccinated. The more people we get vaccinated, the less likely we’ll have transmission.”Dr. Paul A. Offit, a professor at the University of Pennsylvania and a member of the F.D.A.’s vaccine advisory panel, said that while it’s important to study the safety and effectiveness of a booster dose to prepare for when it might be needed, the current evidence shows the vaccines are working against the Delta and other variants. He said he thinks it’s unlikely that people in the general population will get booster shots this year.“All the data to date point to the fact that immunity against severe critical illness is relatively long lasting,” Dr. Offit said. “The issue is not whether we can get a third dose. It’s whether we can get the first two doses in people who aren’t vaccinated.”Should I be worried about the Delta variant?The Delta variant now accounts for more than half of all infections in the United States, and the real risks are to the unvaccinated. While the Pfizer vaccine and others in use in the United States are slightly less effective against the Delta variant, all of them still offer significant protection against serious illness or hospitalization from Covid-19.Moderna has said test-tube studies using blood samples from vaccinated people show the vaccine is still highly effective against the Delta variant, which caused only a “modest reduction” in virus-fighting antibodies in the samples. And Johnson & Johnson has released two studies that show its vaccine remains effective against Delta, showing only a small drop in potency.“Roughly 99 percent of people who are hospitalized and killed by this virus are unvaccinated,” Dr. Offit said. “You’re not really trying to prevent asymptomatic or mild symptoms. You’re trying to keep people out of the hospital and out of the morgue. It’s a goal we’ve met remarkably well.”Why not just get a third shot to be sure?Given that large parts of the world still have very low vaccination rates, and vaccine supplies are limited, most public health experts say it’s shortsighted to give additional doses to people in wealthy countries who are fully vaccinated. In the United States, nearly 50 percent of all residents are fully vaccinated. But in India, only about 5 percent of the population is fully vaccinated. In much of Africa, fewer than 1 percent of people are vaccinated. The concern is that the longer large parts of the world remain unvaccinated, the greater the risk that new, more threatening variants will emerge.“American lives continue to be at risk if there are large outbreaks elsewhere with more variants being created,” said Dr. Ashish K. Jha, dean of the Brown University School of Public Health. “Even if you take a very narrow lens that you only care about the lives of Americans, there’s still a very compelling argument that a first shot for an Indian person does more good for America than a third shot for an American.”In a news conference on Monday, the leader of the World Health Organization pushed back against Pfizer’s plan to seek authorization for booster shots. “The priority now must be to vaccinate those who have received no doses and protection,” Tedros Adhanom Ghebreyesus, the W.H.O. director general, said.Who will be first in line to get booster shots once they are approved?Some countries are already giving booster doses of vaccine to people with compromised immune systems, including people who have undergone cancer treatment or those who have had organ transplants. Since April, health care providers in France have routinely given a third dose of a two-dose vaccine to people with certain immune conditions. On Monday, Israel also announced it would give a third dose of vaccine to highly vulnerable adults.In addition, Moderna is gearing up to test a third dose in 120 organ transplant recipients, and Pfizer, which produces some medications that suppress immunity, is planning a study of 180 adults and 180 children with compromised immune systems.An estimated 5 percent of the U.S. population is considered to be immunocompromised because of health conditions or drug treatments. While it may be months before booster shots are recommended for the general population, if at all, it’s possible federal health officials will approve an extra shot for a select group of vulnerable patients with compromised immune systems.Dr. Jha said the medical community was waiting for guidance from the C.D.C. and the F.D.A. about whether to give booster doses to people who are immunocompromised and did not develop adequate protection after a standard course of vaccination. “There are some data emerging that a third shot helps those people,” Dr. Jha said. “It really requires the engagement of your specialist. I think most physicians are saying hold. They’d like to see the C.D.C. recommendations on this.”

At-home rapid Covid-19 tests can offer unique benefits for weddings, parties, travel or for households with children or at-risk adults.Got the sniffles? Worried about that night out in a crowded dance club? Or maybe you just want to visit grandma but are concerned about her risk, even though you’re vaccinated.At-home rapid Covid tests — which allow you to swab your own nose and get the results in minutes — can be a useful and reassuring way for both the vaccinated and unvaccinated to navigate the ongoing pandemic.With the availability of vaccines for all people 12 years and older in the United States, it may be hard to imagine why anyone would still need a home test for Covid-19. But the coronavirus isn’t going away anytime soon, and a rise in infections this fall among the unvaccinated appears inevitable as a new, highly-infectious variant called Delta spreads around the world.In most cases, regular home testing isn’t necessary for someone who is fully vaccinated. The current crop of vaccines available in the United States have been shown to be effective against the variants, including Delta. But no vaccine is 100 percent protective, and breakthrough infections, though rare, continue to occur.A home test can offer reassurance to a vaccinated person who has traveled recently or spent time in a crowded bar. It can be used more frequently for families with young children who aren’t yet eligible for vaccination. Home tests are also useful for anyone with an at-risk family member or for people who, for whatever reason, remain unvaccinated.“The most important aspect of these tests is the rapid result,” said Dr. Michael Mina, an assistant professor of epidemiology and immunology at the Harvard T.H. Chan School of Public Health. “Waiting two to three days for laboratory test results isn’t ideal when you need results quickly to make decisions about going to school, work or a social gathering.”Dr. Mina, who championed the use of rapid testing at the height of the pandemic, said that more people should think about using at-home, rapid testing to keep children, the old and at-risk and the unvaccinated safer in the coming months.“As long as the virus is raging in other parts of the world, the risk is too high to completely let down our guard with testing,” Dr. Mina said. (Dr. Mina consults with a new home-testing company that doesn’t yet have any products on the market.) “Unvaccinated people will continue to spread the virus, which happens often without showing any symptoms. And while it’s much less likely, even vaccinated individuals can become infected.”Here are some scenarios where a rapid home test might be useful for vaccinated or unvaccinated people.For unvaccinated children, who could be tested periodically before going to camp or school or right before a birthday party.To regularly check and protect the health of a babysitter who spends time with your unvaccinated children or a home-health aide who is caring for a high-risk individual.As an added precaution for a vaccinated person who wants to spend time with a grandparent or someone who is immune compromised. (An unvaccinated person shouldn’t spend time indoors with a person at high risk.)After traveling on an airplane or spending time in an airport or a crowded bar. (While a vaccinated person does not need to be regularly tested after travel, a home test could be used as a precaution after spending extended time indoors with people whose vaccination status isn’t known.)To be sure a cough or sniffle is just allergies or a common cold rather than Covid-19.To test houseguests before a dinner party or overnight stay, if someone in the group is unvaccinated or at high risk.For guests at weddings or other large gatherings if they can’t provide proof of vaccination.There are two types of home tests that are authorized for use in the United States that give you results on the spot: a rapid antigen test, and a rapid molecular test.Rapid antigen tests are the least expensive (about $12 per test) and are available in retail stores and online. (They typically aren’t covered by insurance.) The BinaxNOW test, made by Abbott, contains two rapid antigen tests per box and costs around $24. To take the test, just swirl the swab in both nostrils and place in a special card. After 15 minutes, the result reads much like a pregnancy test: two pink lines indicate you’re positive for Covid-19. The QuickVue At-Home test, from Quidel, is similarly priced. After swabbing your nose, dip the swab in a solution in a test tube, and then in a test strip. You’ll get results in about 10 minutes.The rapid antigen tests are less reliable for finding Covid-19 in people with low viral loads compared to the “gold standard” P.C.R. tests you’d get from a health care provider. One study found that a rapid home antigen test had a 64 percent chance of correctly spotting the virus in people with symptoms who had tested positive on a P.C.R. test. (The test caught only about 36 percent of those who had the virus but didn’t have symptoms.)But don’t be dissuaded by those numbers. The affordable rapid antigen tests provide a reliable quick check to identify people with infectious levels of virus. For example, let’s say you want to invite friends into your home who are unvaccinated or who have an unvaccinated child. Before hosting an indoor gathering, you can reduce the risk of asymptomatic spread and infection by 90 percent or more if all guests use a rapid antigen test within an hour before the event, said Dr. Mina.Rapid testing can also be used as an added layer of protection before spending time with people who are at high risk of complications from Covid-19, such as those with immune problems or undergoing cancer treatments. Neeraj Sood, a professor and vice dean for research at the University of Southern California and director of the COVID Initiative at the U.S.C. Schaeffer Center, said that even though he’s vaccinated, he would use rapid testing to take extra precautions around such people.“If I was going to hang out in an enclosed space with a friend who’s getting chemotherapy and hasn’t gotten the vaccine, then I would do two tests,” Dr. Sood said. He would take one rapid antigen test three or four days before visiting the friend, and another test the same day of the visit. “If both are negative, I’m very confident I don’t have Covid, and I’m not going to transmit it to my friend,” he said.Rapid testing could also be used to make a small family indoor gathering or a child’s birthday party that included a mix of vaccinated and unvaccinated people safer. “If you put that extra layer in of home testing, I think you’re all making each other more safe,” said Irene Peterson, a professor of epidemiology and health informatics at University College London. “Or you could decide not to have the party.”If you want more certainty than a rapid antigen test can provide, you can consider a more costly rapid home molecular test. These tests work by detecting the virus’s actual genetic material (RNA) and amplifying it to determine if you’re infected. A home rapid molecular test works nearly as well as the P.C.R. tests given at testing centers that are processed by a laboratory, but they are also more expensive than the home antigen tests. Lucira makes a highly-accurate molecular test for $55 that uses nasal swabs and a battery-powered processing unit that provides results within 30 minutes.When would the cost of a rapid molecular test make sense? Families planning a wedding may have loved ones who aren’t vaccinated. (Some people are not fully vaccinated because of health conditions or because they had a bad reaction to the first dose.) For wedding guests who can’t provide a vaccination card or a lab-based negative P.C.R. test result taken within 36 hours of the event, you could ask them to take a home-use rapid molecular test. (You’ll have to work out who will pick up the tab for the test.)Dr. Mina noted that for a large event like a wedding that stretches over a few days, a molecular test would be more reliable than a rapid antigen test because it can detect an early infection as much as 48 hours before an antigen test will turn up positive, he said.Home tests also can be useful during cold and flu season to determine if someone with cold or flu symptoms actually has Covid-19.“Home testing is a great way to keep the virus from spreading within your home if someone is sick or was potentially exposed,” said Daniel Larremore, assistant professor in the department of computer science and the BioFrontiers Institute at the University of Colorado Boulder.Dr. Mina said he hopes more people consider the combined benefit of vaccination and home testing to keep people safer and get back to their routines while the virus is still out there. “The re-emergence of other respiratory viruses, like R.S.V. and influenza, will surely create challenges again this fall and winter,” he said. “If we want to return to normalcy and protect ourselves, accessible and accurate home testing should be one tool that we use and rely on to keep ourselves and loved ones safe.”

The Times’s longtime Personal Health columnist and the nation’s most famous doctor met recently to talk about life as octogenarians and beyond. Listen to their conversation.If you want advice about staying healthy in your 80s, who better to ask than two 80-year-olds who have dedicated their careers to public health?Recently Jane E. Brody, who has written The Times’s Personal Health column for 45 years, and Dr. Anthony S. Fauci, who for 37 years has led the National Institute of Allergy and Infectious Diseases, met via Zoom for the first time to talk about living well as octogenarians. They shared laughs, talked about the challenges of exercising with a security detail and offered advice for thriving as you age.“Take care of yourself, get some reasonable sleep, don’t get overcome by stress, a good diet,” said Dr. Fauci, who turned 80 in December 2020. “Enjoy life, but don’t do things in excess. Exercise is really important. I think that the fact that I’ve been a marathon and 10K runner for the last multiple decades has been very important in my staying fit, looking fit and feeling fit.”Ms. Brody, who celebrated her 80th birthday this month, agreed. “I think you have to continue doing that,” she said. “People ask me, ‘How do you do it?’ I said, ‘Well, I don’t stop.’ If you stop, it’s all over. Don’t stop. Keep going, keep going.”Listen to their conversation.Jane Brody and Dr. Tony Fauci Discuss Life After 80What’s the secret to healthy aging? What was life like growing up in 1940s Brooklyn? Does retirement loom? Those answers and more in a lively conversation with Jane and Tony.

Studies show that moments of disruption offer a unique opportunity to set and achieve new goals. The 10-day Well challenge will help you get started.If there was ever a perfect time to make a life change, this is it.Behavioral scientists have long known that times of disruption and transition also create new opportunities for growth and change. Disruption can come in many forms, and it happens when life knocks us out of our normal routines. It can be moving to a new city, starting a new job, getting married or divorced or having a child. And for many of us, there’s never been a bigger life disruption than the pandemic, which changed how we work, eat, sleep and exercise, and even how we connect with friends and family.“I think this fresh start is really a big opportunity,” said Katy Milkman, a professor at the Wharton School and author of the new book “How to Change: The Science of Getting From Where You Are to Where You Want to Be. “I don’t know when we’ll have another one like it. We have this blank slate to work on. Everything is on the table to start fresh.”Much of Dr. Milkman’s research has focused on the science of new beginnings, which she calls “the fresh start effect.” Dr. Milkman and her colleagues have found that we’re most inclined to make meaningful changes around “temporal landmarks” — those points in time that we naturally associate with a new beginning. New Year’s Day is the most obvious temporal landmark in our lives, but birthdays, the start of spring, the start of a new school year, even the beginning of the week or the first of the month are all temporal landmarks that create psychological opportunities for change.In one study, Dr. Milkman found that students were most likely to visit the gym around the start of the week, the first of the month, following birthdays or after school breaks. Another study found that “fresh start language” helped people kick-start their goals. In that study, people were far more likely to start a new goal on a day labeled “the first day of spring” compared to an unremarkable day labeled “the third Thursday in March.” (It was the exact same day, just labeled differently.)Another study found that when people were advised to start saving money in a few months, they were less likely to do so than a group of people told to start saving around their birthday that was also a few months away. The birthday group saved 20 to 30 percent more money.For many people, the lifting of pandemic restrictions and getting vaccinated means planning vacations and returning to more-normal work and school routines. It’s exactly the kind of psychological new beginning that could prompt the fresh start effect, said Dr. Milkman.“We have this opportunity with this blank slate to change our health habits and be very conscientious about our day,” said Dr. Milkman. “What is our lunch routine going to look like? What is our exercise routine? There’s an opportunity to rethink. What do we want a work day to look like?”It’s Not Too Late to Reset.As the pandemic recedes, some people are worried that the past year of lockdowns, restrictions and time at home was a missed opportunity. Leslie Scott, a nonprofit event organizer in Eugene, Ore., said she feels that she just muddled through a stressful year, rather than using the time to make meaningful life changes.“I sometimes wonder if I squandered this gift of time,” said Ms. Scott, who is an organizer of the Oregon Truffle Festival. “I have all this anxiety that we’re just going to go back to what people think of as normal. As we come out of our cocoons, am I emerging from something and moving toward something new? Or am I just stuck?”While some people did develop healthy new habits during pandemic lockdowns, it’s not too late if you spent your pandemic days just getting by. The good news is that the end of the pandemic is probably a more opportune time for meaningful change than when you were experiencing the heightened anxiety of lockdowns.“Covid-19 was an awful time for many of us,” said Laurie Santos, a psychology professor at Yale who teaches a popular online course called “The Science of Well-Being.” “There’s lots of evidence for what’s called post-traumatic growth — that we can come out stronger and with a bit more meaning in our lives after going through negative events. I think we can all harness this awful pandemic time as a time to get some post-traumatic growth in our own lives.”So What’s Your Next Chapter?One of the biggest obstacles to change has always been the fact that we tend to have established routines that are hard to break. But the pandemic shattered many people’s routines, setting us up for a reset, Dr. Santos said.“We’ve all just changed our routines so much,” she said. “I think many of us have realized during the pandemic that some of the things we were doing before Covid-19 weren’t the kind of things that were leading to flourishing in our lives. I think many of us were realizing that aspects of our work and family life and even our relationships probably need to change if we want to be happier.”One reason fresh starts can be so effective is that humans tend to think about the passage of time in chapters or episodes, rather than on a continuum, Dr. Milkman said. As a result, we tend to think of the past in terms of unique periods, such as our high school years, the college years, the years we lived in a particular town or worked at a certain job. Going forward, we’re likely to look back on the pandemic year as a similarly unique chapter of our lives.“We have chapter breaks, as if life is a novel — that is the way we mark time,” said Dr. Milkman. “That has implications for the psychology of fresh starts, because these moments that open a new chapter give us a sense of a new beginning. It’s easier to attribute any failings to ‘the old me.’ You feel like you can achieve more now, because we’re in a new chapter.”Take the Fresh Start Challenge!While the start of a new chapter is a great time for change, the pages will turn quickly. Now that we’re emerging from the restrictions of pandemic life, social scientists say it’s an ideal time to start thinking about what you’ve learned in the past year. What are the new habits you want to keep, and what parts of your prepandemic life do you want to change?“It’s time to rethink your priorities,” said Dr. Milkman, who outlines more detailed steps for change in her new book. “We have to ask ourselves, ‘How am I going to schedule my time?’ We have a limited window to be deliberate about it, because pretty quickly, we’ll have a new pattern established, and we probably won’t rethink it again for a while.”A good first step is to take our 10-Day Fresh Start Challenge. Sign up, and starting Monday, May 17, we’ll send one or two messages a day to prompt moments of mindful reflection, build stronger connections and take small steps toward building healthy new habits. You can text us, too! The challenge will include 10 daily challenges, with a break over the weekend.To sign up, just text “Hi” or any word to 917-809-4995 for a link to join. (Message and data rates may apply.) If you prefer not to text or live outside the United States, you can follow along on the website or app. Just bookmark nytimes.com/well and join us on May 17 for the first challenge.“I think a lot of us have realized how fragile some of the things were that gave us joy before, from going to the grocery store, to going out to a restaurant with friends, going to a movie, giving your mom a hug whenever you’d like,” said Dr. Santos. “My hope is that we’ll emerge from this pandemic with a bit more appreciation for the little things in life.”