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 international 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 whole lineage—one in every of solely 4 flu teams focused by seasonal influenza vaccines—went fully darkish, seemingly extinct.
Researchers famous the absence final 12 months because the flu was nonetheless struggling to get better 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 response to 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 major varieties of seasonal flu have been circulating globally amongst people lately. 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 clarification of influenza, take a look at 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 might be simpler to match future vaccines to circulating viruses, making seasonal photographs simpler. Then again, a shock re-emergence of B/Yamagata might grow to be extra harmful as time passes and other people lose immunity. However, earlier than well being specialists can recreation out future influenza seasons, they’d prefer to know if B/Yamagata is actually gone.
In an article revealed this week within the journal Eurosurveillance, researchers within the Netherlands sifted by the most recent international influenza surveillance knowledge as much as August 31, 2022, on the lookout for the lacking pressure. They be aware that GISAID, a world database of influenza virus genetic sequences that sometimes will get hundreds of flu sequences every year, has not obtained a single B/Yamagata sequence with specimen assortment knowledge after March 2020.
The World Well being Group’s FluNet surveillance knowledge has had a small variety of reviews of the lacking lineage—43 in 2021, principally from China, and eight sporadic instances from 4 international locations in 2022. For comparability, there have been greater than 51,000 detections of B/Yamagata in 2018.
The authors counsel the small variety of instances within the final two years could also be faulty detections. Quite than circulating viruses, they could merely be detecting signatures of B/Yamagata from vaccines that carry live-attenuated influenza viruses. Or, they might be genetic contamination from inactivated-virus vaccines. This is not only a hypothetical. The authors be aware that numerous B/Yamagata detections within the US and Scotland had been discovered to be from live-attenuated influenza vaccines reasonably than actual instances of circulating virus.
The researchers name for flu surveillance laboratories to extend efforts to detect any Yamagata instances to find out if it is really gone or simply mendacity low. “From a laboratory perspective, we expect it could be advisable to extend the aptitude and capability to find out the lineage of all detected influenza B viruses world wide as that is vital 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 might be declared “extinct” and what the results of what that declaration could be.