The cases, which have yet to be confirmed, were identified in farmworkers culling infected birds. The risk to the public remains low, health officials said.Three workers at a poultry farm in northeast Colorado have preliminarily tested positive for bird flu, according to state health officials.The workers had been culling birds from an infected population at the farm, the Colorado Department of Public Health and Environment said on Friday. All three workers had direct contact with infected birds and were experiencing mild symptoms, including conjunctivitis and “common respiratory infection symptoms,” the department said.The results are preliminary, and the tests have been sent to the Centers for Disease Control and Prevention for confirmation, the C.D.C. said.So far, four farmworkers in the United States have been infected with the virus, called H5N1, which is tied to a continuing outbreak among dairy cattle in several states.One case has been reported in Colorado, another in Texas and two more in Michigan, according to the C.D.C. All of those cases involved direct exposure to dairy cows, according to the state and federal health authorities, and officials have said that there is no evidence that the H5N1 virus spreads easily among humans.The risk to the public remains low, the C.D.C. said, but the agency added that it had sent a team to Colorado at the state’s request to help investigate.The C.D.C. said that it would look into whether workers were wearing personal protective equipment. Farmworkers are advised but not required to wear such equipment, including masks, safety goggles and gloves.“These preliminary results again underscore the risk of exposure to infected animals,” the C.D.C. said of the three new cases in Colorado. “There are no signs of unexpected increases in flu activity otherwise in Colorado, or in other states affected by H5 bird flu outbreaks in cows and poultry.”Avian influenza refers to a group of flu viruses primarily adapted to birds. The virus infecting farmworkers, H5N1, was first identified in 1996 in China and reported in people in 1997 in Hong Kong. A new form of H5N1, which surfaced in Europe in 2020, has rapidly spread around the world, and an outbreak in the United States has affected more than 99 million birds.The outbreak has been spreading among dairy farms since at least March, and 152 dairy herds in 12 states have tested positive for the virus. Scientists are researching how the virus is being transmitted through cows.The virus has also spread to a wide array of animals, including marine mammals like seals and bottlenose dolphins, skunks, squirrels and even domestic cats.

The C.D.C. has stopped distributing the 3-by-4-inch cards, a mainstay of American wallets in the earlier days of the pandemic.The paper Covid vaccination cards were, for a time, a mainstay of American wallets — pulled out before bouncers, inspected at airport desks and shared with pride on social media accounts.But the days of the paper cards are over. The Covid-19 cards will “no longer be given out,” Dave Daigle, a spokesman for the Centers for Disease Control and Prevention, said in a statement Thursday, explaining that the distribution of the vaccine had transitioned from the federal government to commercial hands.People receiving vaccinations will still receive a fact sheet with information about the vaccine, he added, and state health departments will still hold a digital or paper copy.This makes the cards a relic of the bleaker days of the pandemic, when they were handed out as part of a mass vaccination campaign. They became a valuable document representing not only some physical protection against Covid 19 but also access to a myriad of social activities.Given after the first vaccination, the card detailed the manufacturer of a vaccine, the dose numbers, the date and location each shot was administered, and any follow-up shots.As vaccinations were administered across the United States beginning in December 2020, the cards became a coveted symbol for many recipients that they might avoid the worst symptoms of the virus. People took selfies with their card, sharing them online to support a public health campaign that some Americans were hesitant to embrace and that some outright rejected. (Some authorities warned people to stop sharing their card information online, saying that they were possibly giving valuable personal information to identity thieves.)In summer 2021, as officials began lifting lockdown restrictions on public venues, the paper cards took on extra meaning, becoming a ticket in some areas to social gatherings and to some international travel. Much like keys and IDs, they were a constant companion, flashed in front of bars, restaurants and concert venues that required them for entry. But the benefits they offered also raised questions of whether it would cause divisions in society between those were vaccinated and those who were not.In some communities, gyms mandated them to enroll in group classes, and sports stadiums added sections for the vaccinated. Airlines and cruise companies asked to see the cards before travelers could visit certain countries.And they created a market for opportunists: Scammers forged or stole copies of the cards, selling them illegally for up to $60 a piece. Other enterprising minds, cognizant that the 3-by-4-inch cards were slightly too awkward to fit unfolded in a wallet, came up with protective cardholders, both functional and bedazzled.The paper pass became increasingly outdated in the United States and abroad as digital health passes replaced them. And as travel restrictions were lifted in most places — the United States stopped requiring proof of vaccination for international travelers this May — even the digital health passes have largely been phased out.More than 270 million people have received at least one dose of a vaccination, according to the C.D.C.’s tracker. With updated Covid vaccines now on the market and a risk of a surge in infections this fall and winter, the C.D.C. last month recommended that all Americans 6 months and older receive at least one dose of the latest shots.Pharmacies have confirmed that people do not need to bring the old paper cards, long lost for many people, to receive a new vaccine. But the C.D.C. has also recommended keeping vaccination records when possible to give to health providers.Those with a paper card may still want to hold onto it — for practical, if not sentimental, reasons.