WHO says flu vaccines should ditch strain that vanished during COVID

Enlarge / Influenza virus. Image produced from an image taken with transmission electron microscopy. Viral diameter ranges from around 80 to 120 nm. (credit: Getty | BSIP)

The World Health Organization on Friday recommended ditching a common component of seasonal influenza vaccines that protects against a particular strain of the virus—because that strain appears to no longer exist.

Influenza viruses in the B/Yamagata lineage have not been detected since March 2020, when the pandemic coronavirus, SARS-CoV-2, was mushrooming around the world. SARS-CoV-2's explosive viral transmission and the health restrictions that followed drastically disrupted the spread and cycles of other infectious diseases, with seasonal flu being no exception.

The 2020-2021 flu season was virtually nonexistent, and the genetic diversity of circulating flu strains dramatically collapsed. But the B/Yamagata lineage looks to have taken the hardest hit. While other strains rebounded in the years since, causing an early and fierce 2022-2023 season in the US, B/Yamagata remains missing globally, appearing extinct.