In 2009, global health officials started tracking a new kind of flu. It appeared first in Mexico, in March, and quickly infected thousands. Influenza tends to kill the very young and the very old, but this flu was different. It seemed to be severely affecting otherwise healthy young adults.
American epidemiologists soon learned of cases in California, Texas, and Kansas. By the end of April, the virus had reached a high school in Queens, where a few kids, returning from a trip to Mexico, had infected a third of the student body. The Mexican government closed its schools and banned large gatherings, and the U.S. considered doing the same. “It was a very scary situation,” Richard Besser, who was then the acting director of the Centers for Disease Control and Prevention, told me. Early estimates suggested that the “swine flu,” as the new strain became known, killed as many as fourteen per cent of those it infected—a case fatality rate more than two hundred times higher than typical seasonal flu. The virus soon spread to more than a hundred and fifty countries, and the Obama Administration considered delaying the start of school until after Thanksgiving, when a second wave could be under way. Manufacturers worried about vaccine supplies. Like most flu vaccines, the one for the swine flu was grown in chicken eggs. “Even if you yell at them, they don’t grow faster,” Tom Frieden, who replaced Besser as the director of the C.D.C., said, at a press conference.
In the end, the world got lucky. The early stats were misleading: although swine flu was extremely contagious, it wasn’t especially deadly. Sometimes the reverse is true. Avian flu, which spread across the world during the winter of 2005-06, is not particularly transmissible but is highly lethal, killing more than half of those it infects. Each flu virus has its own epidemiological profile, determined by its genetic makeup, and flu genes shift every year. Howard Markel, a physician and historian of epidemics who, in the early two-thousands, helped invent the concept of “flattening the curve,” compared influenza’s swappable genetic components to “two wheels of fortune.” A double whammy—ease of spread combined with lethality—could make COVID-19, or even the 1918 flu, which killed between forty million and a hundred million people, look like a twenty-four-hour bug. [Continue reading…]