This story, like the virus it is about, continues to evolve. This article summarizes some of the recent findings and opinions that are related to the highly pathogenic avian influenza H5N1, but this situation may change at any time.
As of early 2025, over 300 million birds - wildlife along with commercial and backyard poultry flocks - have been infected and have died or been culled from the highly pathogenic avian influenza H5N1 in 108 countries around the world. This virus has also spread to a huge array of other animals, including pigs, tigers, donkeys, and foxes, for some examples. It is also now infecting some domestic animals, such as cats in California who were infected by raw cat food.
Although some farm workers in the United States have been infected with H5N1 because the virus has also begun to infect dairy cattle, these workers have recovered and have not passed the virus on to other people. There were 66 confirmed cases and seven probable cases of H5N1 in the US in 2024. These infections have been caused by direct contact with either infected birds (which are carrying a genetic type of H5N1 known as D1.1) or infected dairy cows (which carry B3.13).
In November 2024, serological evidence reported by the Centers for Disease Control and Prevention (CDC) had suggested, however, that about seven percent of US dairy workers had evidence of recent infection with H5N1 by that time.
In two other cases, one in Canada and one in Louisiana, there were mutations in the virus in human patients who carried the infection. While neither individual passed the virus onto another person, it appears that the virus is adapting to infect human cells in some cases. There is also a wealth of other evidence that the virus is adapting in cattle and is improving its ability to infect people.
Some researchers suspect that if a pandemic will occur because of this virus, the time is now. On the other hand, critical mutations that would be required for the virus to easily infect human cells have not been detected, yet. There might also be other mutations that would be necessary for human infection that researchers are not aware of, or for other molecular reasons, the virus will not adapt in that way. We still don't know how it may change in the future, however.
Experts from the National Institutes of Health have continued to stress that this virus still presents a low risk to most people, and that we have enough treatments to deal with cases that may arise. There are also some vaccines for this virus, and others are in development that could help prevent any potential human pandemic. Right now, health officials at the NIH and a division of the NIH known as the National Institute of Allergy and Infectious Diseases (NIAID) are continuing to monitor the situation.
However, others have stressed the need for vigilant surveillance, more stringent countermeasures, and better preventative efforts. Writing in the New Englad Journal of Medicine, scientists wrote that, "a balance between enhanced vigilance and “business as usual” is needed."
The US Department of Health and Human Services (HHS) has also announced that $306 million in funding is now being awarded to support the US response to H5N1. Most of this money will be intended for preparedness efforts, such as ensuring that hospitals have adequate supplies, training, and diagnostic testing kits.
Other research has also suggested that humans have some protection to this virus already because of multiple previous exposures to other flu viruses, and the immune system's ability to fight different versions of the same virus.
Sources: NIH, CIDRAP, New England Journal of Medicine, mBio, La Jolla Institute for Immunology, CDC, HHS
