Has covid reduced the diversity of influenza viruses?

The pandemic measures may have wiped out some strains of the flu virus – if that were true it would be easier to formulate a vaccine.

Mitigation strategies deployed against covid may have led to the extinction of two strains of the human influenza virus. Masks, distancing, hand washing and closing international travel have limited the circulation of influenza viruses to such an extent , Trevor Bedford, a computational biologist at the Fred Hutchinson Cancer Research Center in Seattle, told STAT News that two subgroups of these pathogens could be definitively gone . The reference is one of the H3N2 virus clades and one of the two lineages

of influenza B viruses, known as B / Yamagata: neither of them has been seen since March 2020, a period from which the last appearance of both in the international databases that trace the evolution of influenza viruses dates back , and they are used to update vaccines every year .

GENEALOGICAL TREE. There are two main families of influenza viruses, influenza A and influenza B. The first group includes two subtypes, H1N1 and H3N2. Each of them is in turn divided into many “branches”, the clades, with H3N2 being much more diversified than H1N1: precisely this excessive diversification due to the evolution of the virus in response to our antibodies makes it particularly difficult to predict which ” version “of H3N2 include, annually, in the formulation of the flu vaccine. Influenza B has no subtypes but divides into two lineages (or viral strains ), called B / Victoria and B / Yamagata.

WHAT IF IT WAS A MISTAKE? To trace the last appearance of the B / Yamagata viruses and the 3c3 clade of H3N2 we must go back to March 2020. It is possible that due to the reduced viral circulation the two strains have disappeared permanently from the face of the Earth, but it could also be a ‘ illusion due to the fact that in the last year and a half, priority of testing and genomic sequencing has been given to samples of the SARS-CoV-2 coronavirus, at the expense of everything else.

Even though the 2020-2021 flu season was much weaker than usual, some flu outbreaks still occurred in West Africa, Bangladesh, and Cambodia. Not to mention that the influenza B / Yamagata virus has already had periods of latency in the past followed by a comeback in a big way.

SIMPLER PREDICTIONS. If, on the other hand, the two strains had really disappeared, the work of formulating the flu vaccines for the next season would be facilitated: precisely the diversity of the H3N2 virus had caused a fiasco in the formulation of the 2017-2018 vaccine, which had failed to protect three quarters of the vaccinated against influenza in the USA. While the disappearance of the influenza B / Yamagata virus, if confirmed, could mean a return of the trivalent influenza vaccines (i.e. which protect against a lineage of influenza B only), in use until recently

by Abdullah Sam
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