Enlarge / A bottle of influenza vaccine at a CVS pharmacy and MinuteClinic on September 10, 2021, in Miami. (credit: Getty | Joe Raedle)
The pandemic coronavirus’ debut wrought universal havoc—not even seasonal flu viruses were spared. Amid travel restrictions, quarantines, closures, physical distancing, masking, enhanced hand washing, and disinfection, the 2020-2021 flu season was all but canceled. That meant not just an unprecedented global decrease in the number of people sick with the flu but also a dramatic collapse in the genetic diversity of circulating flu strains. Many subtypes of the virus all but vanished. But most notably, one entire lineage—one of only four flu groups targeted by seasonal influenza vaccines—went completely dark, seemingly extinct.
Researchers noted the absence last year as the flu was still struggling to recover from its pandemic knockout. But now, the flu has come roaring back and threatens to cause a particularly nasty