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 range of circulating flu strains. Many subtypes of the virus all however vanished. But most notably, one complete lineage—considered one of 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 get well from its pandemic knockout. But now, the flu has come roaring again and threatens to trigger a very nasty season within the Northern Hemisphere. Still, the influenza B/Yamagata lineage stays lacking, based on a examine 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 actually 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: Four predominant kinds of seasonal flu have been circulating globally amongst people lately. Two are influenza sort A viruses: subtypes of H1N1 viruses and H3N2 viruses. The different two are influenza sort B viruses: offshoots of the Victoria and Yamagata lineages. (For a extra detailed rationalization of influenza, take a look at our explainer right here.) Current quadrivalent vaccines goal season-specific variations of every of those 4 kinds of flu viruses.

Having fewer flu viruses round means it might be simpler to match future vaccines to circulating viruses, making seasonal photographs more practical. On the opposite hand, a shock re-emergence of B/Yamagata might develop into extra harmful as time passes and other people lose immunity. But, earlier than well being specialists can recreation out future influenza seasons, they’d prefer to know if B/Yamagata is actually gone.

Vanished virus

In an article revealed this week within the journal Eurosurveillance, researchers within the Netherlands sifted by the most recent international influenza surveillance information as much as August 31, 2022, in search of the lacking pressure. They be aware that GISAID, a world database of influenza virus genetic sequences that sometimes will get 1000’s of flu sequences every year, has not acquired a single B/Yamagata sequence with specimen assortment information after March 2020.

The World Health Organization’s FluNet surveillance information has had a small variety of studies of the lacking lineage—43 in 2021, largely from China, and eight sporadic circumstances 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 circumstances within the final two years could also be misguided detections. Rather than circulating viruses, they might 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 various B/Yamagata detections within the US and Scotland had been discovered to be from live-attenuated influenza vaccines slightly 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 actually gone or simply mendacity low. “From a laboratory perspective, we predict it might be advisable to extend the potential and capability to find out the lineage of all detected influenza B viruses around the globe as that is vital to find out the absence of B/Yamagata lineage viruses,” they conclude. They additionally suggest that the World Health Organization arrange standards to outline when the lineage might be declared “extinct” and what the implications of what that declaration could be.