How Some Strains Of Influenza May Have Gone Extinct During The COVID-19 Pandemic

Contrary to popular belief, influenza as a whole did not completely disappear during the COVID-19 pandemic. That being said, flu activity did drop dramatically during the 2020-2021 flu season, not only in the United States but across the globe, according to the Centers for Disease Control and Prevention (CDC). This was despite high levels of testing. Only 0.2% of respiratory specimens tested in American clinical laboratories came back positive for flu, compared to about 26 to 30% in the three flu seasons prior to the pandemic. Lab-confirmed flu hospitalizations were also at their lowest level since this sort of data started being collected in 2005.

The CDC attributes much of this decline to COVID-19 prevention measures such as staying home, physical distancing, mask wearing, hand washing, and increased ventilation of indoor spaces. The flu is considerably less contagious than COVID-19, according to the CDC, so these measures have been even more effective at reducing flu activity than COVID-19 activity. In addition, millions more Americans got their flu shot in the 2020-2021 season than in previous flu seasons. During the 2020-2021 flu season, some strains of the flu have even virtually disappeared. 

Some flu strains may have even gone extinct

Flu viruses that cause seasonal epidemics fall into two families: influenza A and influenza B. Influenza B is divided into two lineages, B/Yamagata and B/Victoria (per CDC). Not only have flu viruses become much less genetically diverse, but B/Yamagata viruses have not been isolated or sequenced at all since March 2020, according to Nature Reviews Microbiology.

Some experts believe they may have gone extinct, but only time will tell if that is the case. It is not unheard of for lineages belonging to influenza B to occasionally enter a state of dormancy and then re-emerge at a later date. For example, B/Victoria went mostly undetected during the 1990s, only to come back full-force in the early 2000s, the journal explained.

Flu expert Florian Krammer told Stat News that just because B/Yamagata hasn't been detected doesn't necessarily mean it's gone for good, but he holds out hope that it is. With fewer flu strains, it will be easier to make effective flu vaccines in the future.