A pandemic upside: The flu virus became less diverse, simplifying the task of making flu shots
In the eight years leading up to the Covid-19 pandemic, one of the subtypes of influenza A viruses started acting bizarrely. Flu viruses continuously evolve, to evade the immune defenses humans develop to fend them off. But after 2012, H3N2 started to behave differently.
It was almost as if there was a falling out within a family. The viruses formed into factions — clades, in virologists’ language — drifting further and further apart with each passing year and making the process of choosing the version of H3N2 to include in flu shots an increasingly challenging task.
