Science

Two strains of the flu may be completely gone

The measures to fight the pandemic, including in particular the wearing of masks and social distancing, imposed by many countries, have also made it possible to indirectly combat other viruses. This is particularly the case of influenza, for which far fewer cases were reported in 2020. It may even be that two specific strains of influenza have disappeared in the meantime, given the fact that no case of infection concerning these viral strains have only been reported for a year.

There was so little influenza transmission during the COVID-19 pandemic that some types of influenza viruses may be gone. During the COVID-19 pandemic, flu cases have fallen to historic levels – a phenomenon experts attribute to wearing masks and other precautions to fight the novel coronavirus.

The potential disappearance of two viral strains

Interestingly, two types of influenza viruses have not appeared for over a year, which means there have been no reported cases of these viruses worldwide. Experts do not yet know if these types are gone, but if so, authorities may have an easier time choosing which flu virus strains are included in the seasonal flu vaccine.

To explain which influenza viruses may be gone, it helps to understand how influenza viruses are classified. There are two families that cause seasonal influenza: influenza A and influenza B. Influenza A viruses are divided into subtypes based on two proteins on their surface known as hemagglutinin (H) and neuraminidase (N).

Forecasts and circulation pattern for different influenza virus subtypes A for 2019. For more than one, strain 3c3.A (dark blue) has not been reported. © bioRxiv

Currently, H1N1 and H3N2 circulate in humans, and each of these subtypes is further broken down into “clades”. Influenza B viruses, on the other hand, do not have subtypes or clades, but are divided into two lineages known as B / Yamagata and B / Victoria. A clade of H3N2, known as 3c3.A, has not been detected since March 2020. The same is true for the B / Yamagata lineage.

A welcome drop in viral diversity

Each year, scientists prepare the flu shot months before the flu season begins by seeing which strains are circulating around the world, and then predicting which flu strains are likely to be most common over the course of the year. coming season. Lower diversity of the influenza virus means a smaller number of circulating viruses to choose from and a greater chance that the vaccine strains will match those in circulation.

The H3N2 viruses are a particularly diverse group, and before the COVID-19 pandemic, their clades seemed to become more and more genetically diverse each year. So a decline in diversity for this subtype would be a good thing, says Richard Webby, director of the World Health Organization’s Collaborative Center for Studies on the Ecology of Influenza in Animals and Birds.

Webby warns that these types of viruses could still exist even though they have not been reported in official databases. But the dramatic drop in influenza cases this year is likely to bring changes for the disease. ” Without a doubt, this will definitely change something when it comes to the diversity of influenza viruses. The extent to which this changes and how long it will persist are the big question marks. But we’ve never seen this before “.

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