The Flu May Never Be the Same

In March 2020, Yamagata’s trail went cold.

The pathogen, one of the four main groups of flu viruses targeted by seasonal vaccines, had spent the first part of the year flitting across the Northern Hemisphere, as it typically did. As the seasons turned, scientists were preparing, as they typically did, for the virus to make its annual trek across the equator and seed new outbreaks in the globe’s southern half.

That migration never came to pass. As the new coronavirus spread, pandemic-mitigation measures started to squash flu-transmission rates to record lows. The drop-off was so sharp that several flu lineages may have gone extinct, among them Yamagata, which hasn’t been definitively detected in more than three years despite virologists’ best efforts to root it out.

[Read: The pandemic broke the flu]

Yamagata’s disappearance could still be temporary. “Right now, we’re all just kind of holding our breath,” says Adam Lauring, a virologist at the University of Michigan Medical School. The virus might be biding its time in an isolated that some experts are ready to declare it officially done. “It’s been missing for this long,” says Vijaykrishna Dhanasekaran, a virologist at Hong Kong University. “At this point, I would really think it’s gone.”