For most of us, the past two years have been spent wearing masks, washing our hands, and staying away from society to reduce the spread of COVID-19. According to a recent article published in the journal Nature Reviews Microbiology, these measures may have been doing twice as much good as we realized.
It’s an unintended – though certainly welcome – casualty of the world’s improved awareness of disease prevention: researchers at the University of Melbourne are suggesting that certain flu strains might now be extinct. The number and diversity of the surviving strains have been badly hit too, and even certain common cold viruses are feeling the heat.
“The SARS-CoV-2 pandemic has seen a notable global reduction in influenza cases of both influenza A and B viruses,” explain the authors. “In particular, the B/Yamagata lineage has not been isolated from April 2020 to August 2021, suggesting that this influenza lineage may have become extinct, which may provide opportunities for improving availability and effectiveness of influenza vaccines.”
There are four types of flu virus: A, B, C, and D – though as humans, we really only need to worry about A and B, since type C generally causes only mild illness and type D only infects cattle. Influenza A, fast-changing and diverse, is the type that causes pandemics. Influenza B clades – for example, B/Yamagata – tend to be confined to seasonal flu outbreaks.
Despite Influenza B types being slower to evolve, epidemiologists still get to see a few dozen or so new viruses develop per month. Since March 2020, however, there have been no B/Yamagata viruses detected at all. Even certain Influenza A viruses have been reduced, with the number of detections of H1N1 (aka swine flu) and H3N2 viruses dropping an order of magnitude year on year.
“Influenza virus detections dropped dramatically from April 2020, with a ~99% reduction compared with previous years despite roughly similar levels of testing,” the paper confirms. “Behavioural changes (social distancing, mask wearing and hygiene measures) and travel and movement restrictions are thought to be the major factors driving the reduction in influenza incidence, which was also observed for other common respiratory infections such as respiratory syncytial virus.”
It's important not to get carried away here – there’s a chance, the paper warns, that B/Yamagata has “merely gone into hiding.” Influenza B viruses have been known to go “dormant” before, and for surprisingly long time periods too – B/Victoria, the strain which dominated cases in the early 2000s, was barely seen at all through the 1990s.
However, if B/Yamagata really has gone the way of the dodo, it could be very good news for vaccine distribution. Current flu vaccines often aim to protect against four seasonal flu strains: Influenzas A/H1N1, A/H2N3, B/Yamagata, and B/Victoria. Taking B/Yamagata out of this cocktail and moving instead to a three-in-one shot could allow around 200 million more people to receive a vaccine, the paper says.
Alternatively, the authors suggest, vaccines could keep their four-in-one structure, but replace B/Yamagata with a second sub-clade of A/H2N3. That would solve the current annual pharmaceutical dilemma over which sub-clade would be the best choice to protect against in the coming flu season.
“Time will tell whether the B/Yamagata lineage is gone for good,” the paper concludes. “[But] elimination of one of the four current vaccine targets would have favourable implications for annual influenza vaccine reformulation, with opportunities for rational rethinking of optimal strategies to further reduce global influenza burden.”