Publisher Health

If you’re one of the millions of Americans who have already had Covid-19, you may be wondering how long you will have immunity from the coronavirus. Earlier in the pandemic, most people assumed that getting infected had at least one upside: that you would be protected against future encounters with the virus. But as the latest wave heads toward the Western region of the country and the virus shows no signs of easing up, reinfections seem to have become common. Already, many people are reporting second or even third infections with newer variants.

Experts have warned that exposure to the coronavirus — through vaccination or infection — does not mean that you are completely protected from future infections. Rather, the coronavirus is evolving to behave more like its closely related cousins, which cause common colds and infect people repeatedly throughout their lives.

“I’ve thought, almost since the beginning of this pandemic, that Covid-19 is eventually going to become an inevitable infection that everybody gets multiple times, because that’s just how a new respiratory virus gets established in the human population,” said Dr. Amesh Adalja, an infectious-disease specialist at Johns Hopkins University.

However, the coronavirus doesn’t yet fit into clear seasonal patterns like the other common cold viruses. It can also cause debilitating symptoms that persist for months or years in some people, and has claimed the lives of millions of others. So what can you do to protect yourself, not only from infection but also reinfection? We asked experts for answers to common questions.

How long will my immunity last after getting Covid?

Before Omicron, reinfections were rare. A team of scientists, led by Laith Abu-Raddad at Weill Cornell Medicine-Qatar, estimated that a bout with Delta or an earlier coronavirus strain was roughly 90 percent effective in preventing a reinfection in both vaccinated and unvaccinated people. “But Omicron really changed that calculus,” said Dr. Abu-Raddad, an infectious disease epidemiologist.

After Omicron emerged, prior infections only provided about 50 percent protection against reinfection, Dr. Abu-Raddad’s study showed. The coronavirus had acquired so many mutations in its spike protein that newer versions became more transmissible and better able to evade immunity. That means you can catch a version of Omicron after recovering from an older, non-Omicron variant. You can even get sick with one of the newer Omicron subvariants after getting over a different version of it.

Other factors also increase your vulnerability to reinfection, starting with how long it has been since you had Covid. Immune defenses tend to wane after an infection. A study published in October 2021 estimated that reinfection could occur as soon as 3 months after contracting Covid-19. While these findings were based on the genome of the coronavirus and accounted for expected declines in antibodies that could fight off the virus, the study did not account for new variants like Omicron that were radically different from older variants. Because of how different Omicron is, your protection may wane even sooner. In a study published in February that has not yet been peer-reviewed, scientists from Denmark found that some people got reinfected with the BA.2 sublineage of Omicron as soon as 20 days after they got infected with the original Omicron BA.1.

Because the virus is infecting more people now, your chances of being exposed and getting reinfected are also higher, Dr. Abu-Raddad said. And while it’s unclear if some people are simply more susceptible to Covid-19 reinfection, researchers are beginning to find some clues. People who are older or immunocompromised may make very few or very poor quality antibodies, leaving them more vulnerable to reinfection, Dr. Abu-Raddad said. And early research shows that a small group of people have a genetic flaw that cripples a crucial immune molecule called interferon type I, putting them at higher risk of severe Covid symptoms. Further studies could find that such differences play a role in reinfection as well.

For now, you should treat any new symptoms, including a fever, sore throat, runny nose or change in taste or smell, as a potential case of Covid, and get tested to confirm if you are positive again.

Will subsequent infections be more or less severe?

The good news is that your body can call on immune cells, like T cells and B cells, to quash a reinfection if the virus sneaks past your initial antibody defenses. T cells and B cells can take a few days to get activated and start working, but they tend to remember how to battle the virus based on previous encounters.

“Your immune system has all kinds of weapons to try and stop the virus even if it gets past the front door,” said Shane Crotty, a virologist at the La Jolla Institute for Immunology in California.

Many of these immune cells build up their protections iteratively, Dr. Crotty said. That means that people who are vaccinated and boosted are especially well equipped to duke it out with the coronavirus. Similarly, people who have been infected before are able to keep the virus from replicating at high levels if they get reinfected. And most people who have logged encounters with both the vaccine and the coronavirus build up a hybrid immunity that may offer the best protection.

The result is that second or third infections are likely to be shorter and less severe.

Dr. Abu-Raddad, who has been tracking reinfections among large groups of people in Qatar, has already started seeing this promising pattern in patient records: Of more than 1,300 reinfections that his team identified from the beginning of the pandemic to May 2021, none led to hospitalization in an I.C.U., and none were fatal.

But just because reinfections are less severe, it doesn’t mean that they are not terrible. You may still run a fever and experience body aches, brain fog and other symptoms. And there’s no way of knowing if your symptoms will linger and become long Covid, Dr. Adalja said.

It is possible that each Covid infection forces you into a game of Russian roulette, though some researchers hypothesize that the risk is highest right after your first infection. One of the risk factors for long Covid is having high levels of virus in your system early in an infection, and you are likely to have such a high viral load the first time you are infected, Dr. Abu-Raddad said. In subsequent infections, your body is better prepared to fight off the coronavirus so you may be able to keep the virus at low levels until it is completely cleared, he said.

What can you do to reduce your risk of reinfection?

Many of the tools and behaviors that help protect against infection can still help you avoid reinfection, Dr. Abu-Raddad said. “There is no magical solution against Covid reinfection.”

Getting vaccinated and boosted, for example, is a good idea even after you’ve had Covid. You only need to wait a few weeks after an infection to get a shot. The vaccines will bolster your antibody levels, and research shows that they are effective in preventing severe outcomes if you get sick again. “Scientific confidence in vaccine-induced immunity was and is much higher than infection-induced immunity,” Dr. Crotty said.

Additional measures, like masking indoors and in crowded spaces, social distancing and improving ventilation where possible, can provide another layer of protection. But because most people and communities have largely dropped these protections, it is up to individuals to decide when to adopt extra precautions based on their risk of getting Covid and how much they’d like to avoid it.

“If you had an infection just last week, you probably don’t have to mask up,” Dr. Adalja said. “But as a month or so passes from your infection and new variants start circulating in the U.S., it may make sense for high risk individuals to do that. People who are trying to avoid getting Covid because they’re going on a cruise soon or because they need a negative P.C.R. test for some other reason may consider taking precautions. Covid protections don’t have to be one-size-fits-all.”