The US Has Bird Flu Vaccines. Here’s Why You Can’t Get One

As avian influenza rages through birds and dairy cattle across the United States, Georgia has become the latest state to detect the virus in a commercial poultry flock, and on Friday, it halted all poultry sales to mitigate further spread of the disease. Nationally, egg prices are soaring—if you can find them at all in your local grocery store.

The ongoing outbreak in animals has also led to at least 67 human cases of bird flu, with all but one causing mild illness. Earlier this month, a person in Louisiana died after being hospitalized with severe bird flu in December. It’s the country’s first recorded death attributed to H5N1.

The US has previously licensed three H5N1 vaccines for humans, but they’re not available commercially. The government has purchased millions of doses for the national stockpile in case they’re needed. But even as the outbreak spread, federal health officials under President Joe Biden were hesitant to deploy them. Experts say the decision comes down to risk, and currently, the risk of H5N1 remains low. Rolling out a vaccine to farm workers and others at higher risk of infection would be a more targeted tactic, but even that measure may be premature. Now, with a changeover in federal health leadership imminent as President Donald Trump begins his second term, the decision rests with the new administration.

“At the moment, from the point of view of severity and ease of transmission, it does not seem like an imperative to get a vaccine out to protect humans,” says William Schaffner, a physician and professor of preventive medicine at Vanderbilt University in Tennessee.

So far, no person-to-person spread of H5N1 has been identified, but health officials are monitoring the virus for any genetic changes that would make transmission among people more likely. Most bird flu infections are related to animal exposures. Of the 67 known human cases in the US, 40 have been linked to sick dairy cattle and 23 are associated with poultry farms and culling operations. In the other four cases, the exact source isn’t known.

In the US, human cases have been mild, with many of them causing only conjunctivitis. In some cases, people have had mild respiratory symptoms. Aside from the Louisiana patient, all the individuals who tested positive for H5N1 recovered quickly and never needed to be hospitalized. Historically though, H5N1 has been fatal in around 50 percent of cases. Since 2003, a total of 954 cases of human H5N1 have been reported to the World Health Organization, and about half of them died. Egypt, Indonesia, Vietnam, Cambodia, and China have reported the highest number of human bird flu deaths.

Those numbers come with a few caveats. For one, many of those deaths occurred in places where people live very close to the sick poultry. “In those circumstances, the thinking is that they likely got a very large dose of the virus,” Schaffner says.

Plus, the case fatality rate—the proportion of infected people who die from the disease—only takes into consideration known cases, and some cases of H5N1 are no doubt going undetected in part because bird flu symptoms are similar to other respiratory viruses. In the US, language barriers among farm workers, lack of testing, and a reluctance among workers to report that they’re sick are also factors. “We probably miss more cases than we detect, and we’re much more likely to detect a case that’s severe,” says Shira Doron, chief infection control officer for Tufts Medicine in Boston and hospital epidemiologist at Tufts Medical Center.

Doron says vaccination is not the only way to protect agricultural workers and other individuals who might come in contact with infected animals. She says providing personal protective equipment to farms, instructing workers on how to use that PPE properly, and educating the public about not going near sick or dying birds should be the main focus right now. The Administration for Strategic Preparedness and Response, part of the Department of Health and Human Services, manages a national stockpile that has face shields, gloves, respirators, and goggles available to farms that need them. The agency is also making the antiviral drug Tamiflu available to jurisdictions without their own stockpiles to treat symptomatic people with a confirmed or suspected exposure.

After government measures during the Covid pandemic sparked anger and confusion, rolling out a vaccine for H5N1 too soon could do more harm than good. “There are some serious downsides to deploying a vaccine, especially when the risk doesn’t justify it,” Doron says. For instance, if a vaccine would cause side effects in some people who get it, that could erode public trust in the vaccine.

That happened in 1976, when President Gerald Ford ordered mass vaccination against swine flu to head off a pandemic. More than 40 million Americans received the vaccine in record time, but the shot caused a slightly increased risk of Guillain-Barré syndrome, a rare form of paralysis that is usually reversible but occasionally fatal. It was a major blow to trust in public health.

Schaffner says if H5N1 mutates into a form that causes more severe disease or is spread easily from human to human, that should clearly trigger the use of a vaccine.

But Elizabeth Strater, national vice president of United Farm Workers, says person-to-person spread may not be obvious. “We understand that federal experts don’t recommend a vaccine program unless there is proof of person-to-person transmission. That said, there are so many cases in farm workers going unreported it may be difficult to determine exactly when that happens. Since farm workers can’t afford to isolate at home when they are infected, they are continuing to work while sick,” she says.

While three H5N1 vaccines are already in the national stockpile, they were approved in 2007, 2013, and 2020, and were formulated to earlier strains of the virus. Two of those three vaccines have shown that they can generate neutralizing antibodies against the current version of the virus in lab studies. In the event that vaccines are needed, manufacturers are also working on shots that match the current strains circulating in birds and dairy cattle. Last week, HHS under President Joe Biden awarded Moderna $590 million to help fast-track the development of an mRNA vaccine, the same technology used in some of the Covid vaccines.

Whether to use these vaccines will be left up to the Trump administration, and if confirmed, that decision would fall to Trump’s pick for HHS secretary, Robert F. Kennedy. A known vaccine skeptic, Kennedy questioned the need for a human bird flu vaccine on X last July.

A vaccine for animals may be more politically palatable for the new Trump administration. Bird flu can kill poultry in just a few days, and once it is detected on a farm, entire flocks have to be culled. The Department of Agriculture has a national H5N1 vaccine stockpile for use in commercial poultry and said recently that it will add additional vaccines to it that have been updated for the current strain. US poultry producers have long resisted vaccination over fears that vaccinating birds could trigger bans on exported poultry, spark food safety concerns among consumers, and make it harder to detect bird flu outbreaks, since vaccination may not fully prevent infection.

Researchers are also working on H5N1 vaccines for cattle. So far, at least seven candidate vaccines have been approved for field safety trials, according to a USDA announcement. Vaccinating cattle may be more feasible than immunizing poultry, as they live longer than commercial poultry, and dairy herds typically number in the hundreds while commercial flocks can have tens to hundreds of thousands of birds. Vaccinating dairy cattle could prevent some human cases of H5N1 but not all of them, since the virus is so widespread in birds and poultry.

“If we can control, or at least contain, the virus in these reservoir species, then you can prevent the spillover to another species,” says Mahesh Kumar, senior vice president of Zoetis, an animal health company that is developing an H5N1 vaccine for cattle. He thinks the dairy industry will be more open to the idea of vaccination than poultry producers have been. “Dairy cattle are much more expensive,” he says. “There’s a huge impact, economically, for the dairy industry.”

Correction: 1/22/2024, 3:48 pm EST: This story has been corrected to properly identify Mahesh Kumar.