The pandemic coronavirus’ debut wrought common havoc—not even seasonal flu viruses had been spared. Amid journey restrictions, quarantines, closures, bodily distancing, masking, enhanced hand washing, and disinfection, the 2020-2021 flu season was all however canceled. That meant not simply an unprecedented world lower within the variety of individuals sick with the flu but additionally a dramatic collapse within the genetic variety of circulating flu strains. Many subtypes of the virus all however vanished. However most notably, one total lineage—one among solely 4 flu teams focused by seasonal influenza vaccines—went utterly darkish, seemingly extinct.
Researchers famous the absence final 12 months because the flu was nonetheless struggling to recuperate from its pandemic knockout. However now, the flu has come roaring again and threatens to trigger a very nasty season within the Northern Hemisphere. Nonetheless, the influenza B/Yamagata lineage stays lacking, in keeping with a research revealed this week within the journal Eurosurveillance. It has not been definitively detected since April 2020. And the query of whether or not it is really gone extinct lingers.
What B/Yamagata’s absence may imply for future flu seasons and flu photographs additionally stays an open query. For a fast refresher: 4 predominant varieties of seasonal flu have been circulating globally amongst people in recent times. Two are influenza sort A viruses: subtypes of H1N1 viruses and H3N2 viruses. The opposite two are influenza sort B viruses: offshoots of the Victoria and Yamagata lineages. (For a extra detailed rationalization of influenza, try our explainer right here.) Present quadrivalent vaccines goal season-specific variations of every of those 4 varieties of flu viruses.
Having fewer flu viruses round means it could possibly be simpler to match future vaccines to circulating viruses, making seasonal photographs simpler. Alternatively, a shock re-emergence of B/Yamagata may grow to be extra harmful as time passes and other people lose immunity. However, earlier than well being consultants can sport out future influenza seasons, they’d prefer to know if B/Yamagata is really gone.
In an article revealed this week within the journal Eurosurveillance, researchers within the Netherlands sifted by the most recent world influenza surveillance information as much as August 31, 2022, on the lookout for the lacking pressure. They observe that GISAID, a world database of influenza virus genetic sequences that usually will get hundreds of flu sequences annually, has not acquired a single B/Yamagata sequence with specimen assortment information after March 2020.
The World Well being Group’s FluNet surveillance information has had a small variety of stories of the lacking lineage—43 in 2021, largely from China, and eight sporadic circumstances from 4 nations in 2022. For comparability, there have been greater than 51,000 detections of B/Yamagata in 2018.
The authors recommend the small variety of circumstances within the final two years could also be inaccurate detections. Somewhat than circulating viruses, they might merely be detecting signatures of B/Yamagata from vaccines that carry live-attenuated influenza viruses. Or, they could possibly be genetic contamination from inactivated-virus vaccines. This is not only a hypothetical. The authors observe that various B/Yamagata detections within the US and Scotland had been discovered to be from live-attenuated influenza vaccines moderately than actual circumstances of circulating virus.
The researchers name for flu surveillance laboratories to extend efforts to detect any Yamagata circumstances to find out if it is really gone or simply mendacity low. “From a laboratory perspective, we predict it will be advisable to extend the potential and capability to find out the lineage of all detected influenza B viruses world wide as that is crucial to find out the absence of B/Yamagata lineage viruses,” they conclude. In addition they suggest that the World Well being Group arrange standards to outline when the lineage could possibly be declared “extinct” and what the implications of what that declaration is perhaps.