http://www.sciencemag.org/news/2021/01/covid-19-measures-also-suppress-flu-now

Masks, social distancing, and lockdowns to fight COVID-19 seem to have kept other respiratory viruses from spreading.

Influenza forecasters are a cautious bunch. Flu cases can spike in late winter after months of low infection rates, making experts reluctant to predict a mild season too soon. But many are ready to declare that COVID-19 control measures have dramatically tamped down the flu and other respiratory viruses that would normally be ripping through the Northern Hemisphere.