healthHealth and Medicine

COVID-19 Precautions May Have Helped Wipe Out Two Flu Strains


Tom Hale

Senior Journalist

clockJun 7 2021, 17:25 UTC

3D computer-generated rendering of a whole influenza (flu) virus in semi-transparent blue with a navy-blue background. Image Credit: US Centers for Disease Control and Prevention.

There’s some speculation that the past year-and-a-bit of masking up, social distancing, and improved handwashing may have driven a few flu strains out of the human population. They may – and it's a big “may” for now – have effectively gone extinct. 

It’s previously been suggested that the COVID-19 pandemic saw a sharp decrease in flu cases. Early estimates showed that the 2020-2021 flu season was practically non-existent, while many other common communicable infections were also significantly down. It’s now emerged that a number of certain flu strains have not been picked up by any researchers over the past year, indicating they may become extinct in human populations, STAT reports.


According to STAT, one of the H3N2 clades and a lineage of influenza B viruses, known as B/Yamagata, have not been added to any international databases used to keep tabs on the flu virus evolution since March 2020. This could indicate that overwhelmed healthcare systems failed to detect the strains due to a lack of testing – or that the strain has been eradicated from humans thanks to our wider efforts to prevent the spread of COVID-19. 

"I think it has a decent chance that it's gone. But the world's a big place," Trevor Bedford, a computational biologist at the Fred Hutchinson Cancer Research Center in Seattle, told STAT, while speaking about the H3N2 clade.

“There had been maybe five-ish, six-ish [H3N2] clades circulating and now there’s two or three that made it through that bottleneck,” added Bedford. 


To go into a little bit of background, the influenza virus can come in a variety of subtly different forms. There are four types: A, B, C, and D. Human influenza A and B viruses are typically associated with the flu season, while only Influenza A viruses are known to cause flu pandemics.  

Influenza A viruses are then split up once more into subtypes based on two proteins on the surface of the virus: hemagglutinin (H) and neuraminidase (N). For instance, H3N2 refers to the influenza A virus with hemagglutinin subtype 3 and neuraminidase subtype 2. They can then be divided into further clades and subclades. On the other hand, Influenza B doesn’t have subtypes but is split into two lineages: B/Victoria and B/Yamagata

While there is undoubtedly a hell of a lot of troublesome influenza bugs still out there, this recent observation may imply that H3N2 has become somewhat less diverse.


To develop the seasonal flu shot, scientists have to hedge their bets as to what flu strain will be causing problems during the following season. With the help of surveillance centers in over 100 countries across the world, researchers use models to understand the strains that are currently doing the rounds and which threaten to spread when the season hits. It’s a notoriously tricky process and it’s been known for scientists to pick “the wrong one” in years gone by.

H3N2 viruses are especially diverse and mutate rapidly, meaning the process of estimating any problematic strain is extra fiddly. If the H3N2 virus really has become less diverse, then it could make the process of developing a vaccine slightly easier. With that said, it would be naive to make any concrete judgments about the fate of the "missing" strains, so scientists are remaining cautiously optimistic with their predictions.



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  • Influenza,

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