STAT Helen Branswell
The unsettling reality of H5N1 bird flu circulating in dairy cow herds in multiple parts of the United States is raising anxiety levels about whether this dangerous virus, which has haunted the sleep of people who worry about influenza pandemics for more than 20 years, could be on a path to acquiring the ability to easily infect people.
To be clear, there is no evidence that this is currently the case — the sole confirmed human case reported in Texas three weeks ago was in a farm worker who had contact with cattle. There is no way to predict if the virus will acquire the capacity to spread between people, or when and under what conditions it would make that fateful leap if it does.
But the first signs that H5N1 — or any new flu virus — was starting to spread from person to person would trigger a race to produce massive amounts of vaccine to try to mitigate the damage a flu pandemic might be expected to cause. While the 2009 H1N1 pandemic is estimated to have killed about a quarter-million people worldwide — severe flu seasons sometimes kill more — the 1918 Spanish flu pandemic is believed to have killed between 50 million and 100 million people, many times more than Covid-19.
The good news: The world makes a lot of flu vaccine and has been doing it for decades. Regulatory agencies have well-oiled systems to allow manufacturers to update the viruses the vaccines target without having to seek new licenses. The United States even has some H5 vaccine in a stockpile that it believes would offer protection against the version of the H5N1 virus infecting dairy cattle, though there would not be nearly enough doses for the entire country.