In the USA the lockdown was maintained until August 2020. So the lockdown basically existed right up to the flu season. Were you expecting the flu to instantly spike back to baseline levels once lock down ends? It takes time for viruses to start spreading again, it isnt an instant process you know, and with the lockdowns literally ending right as flu season begins means you are going to have a much reduced incident.
Also you are flat out wrong about the 0 flu cases.
It wasn’t just that a somewhat obscure strain was eliminated… here in Alberta, we skipped an entire ‘flu season, with 0 lab recorded cases in 20-21.
Alberta’s 2021 flu season had 2,906 confirmed flu cases resuling in 523 hospitalizations. Anf thats just confirmed cases.