New XBB variant of Covid-19: contagiousness, resistance to vaccines… should we worry about this new strain?

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Many Omicron subvariants have been detected around the world, but scientists are currently closely examining the XBB subvariant, which is more resistant to antibodies generated by vaccination. The Dépêche du Midi takes stock.

He has been alone for several months in the French “epidemic landscape”. The BA.5 subvariant, belonging to the Omicron family, alone carried two waves of contamination linked to Covid-19 in France. At the beginning of the 2022 academic year, no other variant has been consolidated on a European scale, which allows health authorities to fight, once again, against a variant whose properties are well known. However, the scientific community is concerned about a variant called “XBB”, identified in Asia, again from the Omicron line, and likely to spread in Europe. the midi office takes stock of this new discovery.

What do we know about this new variant?

Like any other virus, Sars-Cov-2 replicates and transforms. Today, the scientific community has identified more than 300 sublineages belonging to the Omicron lineage. This is proof that in two and a half years of the pandemic, the virus has mutated many times (see box below). The XBB variant is of this caliber: it is “resulting from a combination of two Omicron sub-lineages”, he explains to the midi office Professor Antoine Flahault, epidemiologist and director of the Institute for Global Health at the Faculty of Medicine of Geneva.

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This new strain is endowed with five characteristic mutations that “allow the subvariants that possess them to overcome the acquired immunity to counteract the adherence of the virus to our cells”, continues the researcher. In practice, XBB could thus more easily infect our body: the variant “would be to date one of the known variants of SARS-CoV-2 that best manages to escape acquired immunity (after contamination, note) or the vaccine ”, explains the epidemiologist. .

Where was this variant detected?

The XBB variant was first detected in Singapore, where it appears to be spreading rapidly and gradually becoming a “dominant strain”. “In Australia, it now represents 5% of sequenced samples, with very fast and very recent growth,” says Professor Antoine Flahault.

In addition, the first cases of contamination have been detected in Europe and the United States: therefore, it is likely that this variant will prevail there in turn, or even “coexist with other sub-variants that seem to share certain common characteristics with XBB. “, continues the researcher.

Would the vaccines used today against this variant still be effective?

Researchers remain confident that immunity from vaccination and immunity from infections due to earlier variants will reduce the risk of severe forms linked to this new variant.

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“Cell-mediated immunity, the one that allows our body to fight against severe forms of Covid, is not, as far as we know, eluded by these new variants, Professor Flahault wants to believe. Vaccines, mono and bivalent (new generation, note from the editor), therefore, it must continue to effectively protect us against the risks of hospitalization and death related to Covid”.

How does a virus mutate?

When it enters a cell, a virus replicates: it copies itself to spread. During replication, errors in the copy of the virus genome can occur, such as a computer “bug”. But this error may or may not have a more or less significant impact on the behavior of the virus: it is about mutations. Therefore, a variant is a virus that carries one or more new mutations of the initial virus.

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