The Covid-19 pandemic killed off one strain of the flu, and that will change the next vaccines

For 10 years, Americans have had access to flu shots that protect against four strains of the virus: two A strains and two B strains.

Starting this fall, however, all the flu shots distributed in the United States will contain only three strains, and the change happened in part because of Covid-19.

On Tuesday, a panel of experts who advise the US Food and Drug Administration on vaccines voted unanimously to recommend three-strain flu vaccines that will exclude any viruses from B strains that are part of branch of the flu’s family tree called Yamagata.

Yamagata viruses were in decline before the pandemic, and all the precautions that helped people avoid Covid-19 – including masking, staying at home and better ventilation – appear to have finished them off. They haven’t been detected in testing since March 2020.

https://edition.cnn.com/2024/03/05/health/flu-vaccine-yamagata-strains/index.html

While masking, staying at home, and better ventilation probably all played a part, I think that frequent hand washing, social distancing and other measure were also important. Masks are mainly important because they limit emission of viral particle by loud talkers. That plus social distancing were probably the most effective. Polite Asians wear masks in public if they have a cold. Northern Europeans have conventionally greater social distancing, likely in order to limit the spread of lice and fleas between people wearing heavy clothing before DDT and other insecticides.