I still think it is pretty remarkable and great that an entire flu lineage seems to have gone extinct during the pandemic. I've seen no reports of B/Yamagata since March 2020. 0 detections this flu season as well, and flu came back with a vengeance this year.
And contrary to COVID skeptics we didn't reduce flu sampling during the pandemic (flu sampling actually increased), so it isn't a detection issue.
For those concerned about bird flu the CDC hasn't seen any signs of concerning mutations that would spark human to human transmission.
Beyond just interesting this also has practical significance as well. It can make the vaccine targeting process easier. The difficulty with influenza is it is constantly mutating, so the virus we are looking at from one season to the next constantly changes.
To be more precise each season we are often dealing with multiple circulating flu viruses at once that change significantly over time. Since mRNA flu vaccination isn't ready for primetime yet we still have relatively long lead times in manufacturing, so we have to select the target vaccine strains around March the year before the next flu season. VRBPAC just had their meeting for strain selection earlier this month in fact.
There are a few influenza clades that haven't been seen since March 2020 as well. We'll have to see if that persists going forward. It seems the pandemic was a bottleneck for flu.
One of the clades I thought went extinct showed up in the 2021-2022 season, so there's always a chance it may be an underdetection issue. But as I said flu sampling actually has increased during the pandemic, so we should have good coverage.
This chart doesn't show the 2022-2023 season. But so far the entire B/Yamagata lineage has not been detected in 3 years now through March 2023