Fact Check: Could Bird Flu Kill One in Four Americans?

A multistate outbreak of avian flu, with one in five commercial milk samples testing positive for genetic traces of the virus, has led to congressional hearings over concerns of the health risk passed to humans.

Highly pathogenic avian influenza (H5N1) is an infectious viral illness that spreads primarily among wild and domestic birds. But the virus that causes bird flu can sometimes jump into other animals, including dairy cows, and, in some cases, humans.

Although risk of infection remains low, a recent Senate committee hearing with a U.S. Food and Drug Administration (FDA) chief led to suggestions that the disease could kill in one in four Americans.

The Claim

A post on X, formerly Twitter, by user WarClandestine posted on May 10, 2024, viewed 269,000 times, included a screengrab from a news article that read "FDA says it's preparing for a bird flu pandemic in people that could kill one in four Americans."

User WarClandestine wrote: "It's starting to look like H5N1 Bird Flu may be 'Disease X.'

"The MSM have been subtly planting the idea in our heads, and now our health agencies are admitting they are preparing for the H5N1 pandemic.

"They are going to try it again...

"Mail-in ballots are their objective."

The Facts

The headline attached to this post is missing some crucial context that alters how it might be understood.

While it may be interpretated that H5N1 virus could kill 25 percent of the American population, that might only be true if everyone was infected with the disease.

As the full story published by the Daily Mail explains, FDA Commissioner Dr. Robert Califf told a Senate Appropriations Committee last week that H5N1 mortality rates among those infected had been 25 percent in other parts of the world.

Califf told senators that the virus was mutating and that the FDA was preparing for a pandemic should it become more infectious.

"We got to have testing, got to have antivirals and we need to have a vaccine ready to go so we've been busy getting prepared for if the virus does mutate in a way that jumps into humans on a larger level," he said.

However, Califf added that the risk to public health was low, with only two human cases of H5N1 reported in the U.S., one of which was detected in Texas after exposure to dairy cattle presumed to be infected.

The data that supports a one-in-four mortality rate also deserves some scrutiny. Dr. Alastair Ward, associate professor of biodiversity and ecosystem management at the University of Leeds, told Newsweek that the statistic was thought to have come from the outbreak of H5N1 in Chinese poultry in the 1990s and had "nothing to do with the current outbreak among U.S. cows, which is a different reassortant of the virus."

"Twenty-five percent was not the population mortality rate, it was the mortality rate of Chinese poultry workers—plucking, gutting and butchering in markets—who showed symptoms of infection during the early 1990s H5N1 outbreak in China, i.e. of those people at very high risk of exposure and who fell ill with high path avian flu, a quarter of them died.

"We have no idea what number or proportion of 1990s Chinese poultry workers were infected but showed minor or no symptoms or were challenged but did not become infected.

"There will have been some within each of these categories, so the mortality rate among 1990s Chinese poultry workers was almost certainly lower than 25 percent, and the Chinese population mortality rate will have been much, much, much lower."

Last month, the World Health Organization (WHO) released data showing that between January 1, 2003, and March 28, 2024, among 254 cases of human H5N1 infection reported in Vietnam, China, Cambodia and Laos, 141 were fatal, meaning the case fatality rate was 56 percent.

However, as Ward told Newsweek,it was likely to have only been among those who presented with symptoms, noting that small sample sizes would create large proportional differences.

"People who don't suffer illness or who suffer mild symptoms tend to stay away from doctors so don't feature in these stats," he said.

"The 254 people presenting with avian flu symptoms over this time do not constitute a random or representative sample of the global human population or even the population exposed to H5N1 during that outbreak, so it is not an estimate of the mortality rate, it's the proportion of a small sample of ill people that died with H5N1 over several years.

"Past human cases have almost exclusively been among those who lived and/or worked very closely with poultry, and usually in situations where hygiene standards were substantially different to those in the U.S. and Europe."

A spokesperson for the FDA provided further data from WHO for 2003-2024 that showed among 888 cases reported to it, 463 of those had died.

The post on X by WarClandestine also hinted at a conspiracy theory based around "Disease X," which is a placeholder name for an unknown virus that could infect humans, first mooted by the World Health Organization.

"Disease X represents the knowledge that a serious international epidemic could be caused by a pathogen currently unknown to cause human disease," WHO said on its website.

The disease could come about in many ways, including as a result of biological warfare or the sudden spread of a virus similar to the "Spanish flu" that affected large parts of the world and is thought to have killed at least 40 million people in 1918-1919.

The WHO also considered adding a number of other diseases to its list of global threats, including arenaviral hemorrhagic fevers, highly pathogenic coronaviral diseases and Chikungunya, a viral disease transmitted to humans by infected mosquitoes.

However, the name "Disease X" has been misused to claim that it is a real disease being concocted by global leaders to enforce political change around the world, a theory based on no evidence and a fundamental misunderstanding of how the term was coined.

The Ruling

Needs Context.

The claim that one in four Americans could die from H5N1 is somewhat misleading. FDA Commissioner Dr. Robert Califf said during a recent Senate hearing that some data shows H5N1 has a one in four mortality rate among those infected. It is not a projection of how many Americans will die should it spread.

The data it is based on is also thought to be old, from infections among Chinese poultry workers in the 1990s.

FACT CHECK BY Newsweek's Fact Check team