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Opinion|This Is the Great Mystery of Bird Flu in America
https://www.nytimes.com/2025/03/25/opinion/bird-flu-america-death.html
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Guest Essay
March 25, 2025
By Caitlin Rivers
Dr. Rivers is an epidemiologist and the author of “Crisis Averted: The Hidden Science of Fighting Outbreaks.”
Bird flu has long been a top contender for starting the next pandemic. Between 2003 and 2023, there were 882 cases reported in humans worldwide, resulting in 461 deaths. This suggested a staggering mortality rate, around 50 percent — a warning of H5N1’s deadly potential.
The vast majority of infections and deaths were before 2020. But a few years of quiet ended in 2024, when America became the epicenter for the world’s human infections. And there was something else about the U.S. cases: They were nowhere near as severe as before.
The virus had been mostly tied to poultry, but in America last year it began circulating in dairy cows as well. Dozens of farmworkers have become infected. And yet, of the 70 human H5N1 cases reported over the last year in the United States, there was only one death. All but a few of the other U.S. cases have been mild, with most infected people experiencing little more than pink eye or a cough. It’s a pattern that is puzzling epidemiologists.
The lower-than-expected death rate has not escaped the notice of the health secretary Robert F. Kennedy Jr., who has cited it as a reason to allow the virus to “run through the flocks” rather than cull and control outbreaks in poultry. That proposal invites disaster. The United States has gotten lucky so far, but that luck might not last.
The one fatality over the last year was in January, when an older adult in Louisiana died after contracting the virus from a backyard flock. Last month, two people with exposure to poultry were hospitalized. And in Canada, which has also experienced outbreaks in birds, a teenager spent weeks in intensive care. These cases are a sharp reminder that the virus hasn’t lost its lethal potential.
Epidemiologists like me are wary of drawing premature conclusions about severity. Small samples can be misleading, and most of the recent cases occurred in dairy farmers. If the virus reaches infants, older adults or people with serious health conditions, it may be more deadly.
But let’s assume that today’s H5N1 is in fact milder compared with past outbreaks in the Middle East and Asia. Why might that be?
