COVID may have pushed a leading seasonal flu strain to extinction

The onset of the pandemic coronavirus wreaked common havoc – even seasonal flu viruses weren’t spared. Amid journey restrictions, quarantines, shutdowns, bodily distancing, masking, enhanced handwashing and sanitizing, the 2020-2021 flu season has been all however cancelled. This meant not solely an unprecedented world lower within the variety of folks with influenza, but in addition a dramatic collapse within the genetic range of circulating influenza strains. Many subtypes of the virus have nearly disappeared. Crucially, nevertheless, a whole lineage – certainly one of solely 4 flu teams focused by seasonal flu vaccines – has gone fully black, seemingly extinct.

The researchers famous the absence final 12 months when the flu was nonetheless struggling to recuperate from its pandemic knockout. However now the flu is again in full drive and threatens to deliver a few notably nasty season within the northern hemisphere. Nonetheless, the influenza B/Yamagata lineage stays lacking, in line with a examine revealed this week within the journal Eurosurveillance. It has not been undoubtedly detected since April 2020. And the query of whether or not it actually disappeared persists.

What the absence of B/Yamagata may imply for future flu seasons and flu vaccines additionally stays an open query. For a fast refresher: 4 predominant varieties of seasonal flu have circulated around the globe amongst people in recent times. Two are kind A influenza viruses: the H1N1 virus and H3N2 virus subtypes. The opposite two are kind B influenza viruses: offspring of the Victoria and Yamagata lineages. (For a extra detailed rationalization of influenza, see our explainer right here.) Present quadrivalent vaccines goal season-specific variations of every of those 4 varieties of influenza virus.

Having fewer flu viruses means it may very well be simpler to match future vaccines to circulating viruses, making seasonal photographs more practical. Alternatively, a shock re-emergence of B/Yamagata may change into extra harmful as time passes and other people lose their immunity. However, earlier than well being consultants can decide future flu seasons, they want to know if B/Yamagata is admittedly gone.

Virus gone

In a paper revealed this week within the journal Eurosurveillance, Dutch researchers sifted via the most recent world flu surveillance information as much as August 31, 2022, on the lookout for the lacking pressure. They word that GISAID, a worldwide influenza virus genetic sequence database that sometimes receives hundreds of influenza sequences every year, didn’t obtain a single B/Yamagata sequence with pattern assortment information after March 2020.

World Well being Group FluNet surveillance information had a small variety of lacking lineage studies – 43 in 2021, largely from China, and eight sporadic instances from 4 nations in 2022. For comparability, there have been over 51,000 detections of B/Yamagata in 2018.

The authors recommend that the small variety of instances over the previous two years may very well be a misdetection. Slightly than circulating viruses, they’ll merely detect signatures of B/Yamagata from vaccines carrying stay attenuated influenza viruses. Or, it may very well be genetic contamination from inactivated virus vaccines. It is not only a speculation. The authors word that plenty of detections of B/Yamagata in the USA and Scotland have been discovered to be from stay attenuated influenza vaccines relatively than precise instances of circulating virus.

Researchers are calling on flu surveillance labs to extend their efforts to detect any instances of Yamagata to find out whether it is actually gone or simply declining. “From a laboratory perspective, we consider it could be fascinating to extend the capability and skill to find out the lineage of all influenza B viruses detected worldwide, as that is important to find out the absence of B/Yamagata lineage virus,” they conclude. Additionally they suggest that the World Well being Group set up standards to outline when the lineage may very well be declared “extinct” and what the implications of this declaration may very well be.