Science

What we know about the “BA.2” strain, Omicron’s cousin that could revive the 5th wave

Some positive signs, the drop in incidence rates in Ile-de-France, have given the illusion of an imminent decline. But the fifth wave of Covid-19 is still far from over. Some 436,167 new infections identified in 24 hours in the territory on Wednesday, after a record of more than 460,000 cases the day before. A question arises: is Omicron, largely in the majority (over 95%), the only one responsible for this (new) rebound in the fifth wave?

A strain, BA.2, very close to Omicron (BA.1), is spreading throughout the world and mainly in Europe. It dominates even in Denmark, a country very active in sequencing, and subject to a very strong wave of contamination. The BA.2 strain was also detected in the UK, Sweden and 40 other countries according to the Gisaid benchmark database Outbreak platform. Including France.

Not all of them are necessarily affected by increased pollution, such as the UK, which is in steep decline. However, suspicion weighs on others, such as France, given the current dynamics of the epidemic and the characteristics of the subvariant.

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No evidence of increased severity

“It reminds me of the situation in mid-December. Our models then predicted a possible peak of the Delta wave, but the Omicron variant came online and there was no decline in France,” epidemiologist Antoine Flahault from LCI notes cautiously. According to the health expert, BA.2 would contain 28 more mutations than Omicron, and based on its rapid progression in Denmark, or even India and Singapore, it could be more contagious than its predecessor.

Nothing says, however, that it is more serious. “In the current state of the data, it is unlikely. The two viruses are close enough at the level of the Spike protein to think that they behave in approximately the same way,” emphasizes Etienne Simon-Lorière in Parisian.

So all variants do not act the same way everywhere on the planet. The newspaper rightly cites the example of the AY.4.2 strain, close to Delta, which for a time accounted for 25% of contaminations in the United Kingdom, without worrying France.

The express

“I wouldn’t be surprised if BA.2 slowly replaces BA.1 over the next few months with a slightly ‘optimized’ mutational profile,” British virologist Tom Peacock of Imperial College London tweeted. Delta to Omicron. The professional evokes a more “subtle” change. The only certainty: During the health crisis, long-term forecasts have rarely proven correct.

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