Bird flu: will our luck run out?

In April of 2024, a young man died in Vietnam after developing severe pneumonia, sepsis, and acute respiratory distress. In June, a toddler returned to Australia after a trip to India. She was admitted to the hospital the next day, and later that week, she was moved to intensive care. Two months later, a previously healthy teenager died in Cambodia. These three young people lost their lives to a virus that has concerned epidemiologists for decades: avian influenza A(H5N1), or bird flu.

In a new essay for the New York Times (that is a gift link), I take on the question of whether H5N1 is more mild than it used to be.

Influenza is a top contender for sparking the next pandemic. Indeed, it has done so before. The infamous 1918 influenza pandemic killed an estimated 50-100 million people, more than World War I and World War II combined. H5N1, in particular, has provoked alarm. Although nearly all cases have been found in people who had close contact with animals, H5N1’s high mortality rate has put it on the map. Between 2003 and 2023, there were 882 reported cases, resulting in 461 deaths. This remarkable mortality rate is a warning of the H5N1’s devastating potential.

Which is why the United States’ experience with the virus is such a puzzle. In 2024, the virus began circulating in dairy cows, the most domesticated of animals to have seen widespread illness from this pathogen. The constant daily human contact required to care for the cows constitutes a bridge between the virus and human populations.

But of the 70 human H5N1 cases reported over the last year in the United States, 95% have been mild. The most common reported symptom is conjunctivitis, or red eyes. Some people have also reported mild upper respiratory symptoms like cough. These cold-like symptoms depart sharply from the severe, often deadly respiratory disease that doctors in Asia and the Middle East have been documenting since 1997. And yet, a recent death of an older adult in Louisiana from H5N1 is a sharp reminder that the virus hasn’t lost its lethal potential.

What accounts for these dramatic differences in outcomes? I go through some of the possibilities over at the NYT. Gift link here

If you like my essays, you’ll probably like my book Crisis Averted: The Hidden Science of Fighting Outbreaks. The Wall Street Journal called it an “ambitious and…successful attempt to reset our relationship with the field of public health. With a judicious blend of candor, hopefulness and pragmatism, [Rivers] calls out its mistakes, reminds us of its historic accomplishments and emphasizes the need for the discipline to adjust its strategies if its full promise is to be realized.”