May 12, 2022

Where is the distribution of the BA.2 sub-variant in France?

If it is still detected at very low levels, this sub-variant of Omicron remains closely watched, in particular because of its probable ability to be transmitted very easily.

“A little cousin of Omicron”. For a few days the term “BA.2” has been regularly mentioned. It is a sublineage of the Omicron variant, which appears to be much more contagious than the BA.1 sublineage, the source of the current fifth wave of infections. BA.2 is detected at very low levels in France for the moment, but it has been identified in several of our neighbors and now represents more than half of the contaminations in Denmark.

In France, “one-off cases spread over different regions were detected by sequencing over the last two weeks of December 2021 and the first two weeks of this year”, but “at very low levels”, writes Santé Publique France in a point dated Tuesday.

How many cases of BA.2 in France?

According to the latest analyzes carried out in France, “out of 10,000 real-life sequencing last week”, the BA.2 variant represented “60 cases”, declared the Minister of Health Olivier Véran Tuesday on LCI.

This figure “is probably underestimated, we probably have a larger number of BA.2”, declared at the same time on FranceInfo the president of the Scientific Council Jean-François Delfraissy. It should indeed be noted that the sequencing analyzes have a delay in France on the epidemic reality, which means that these figures are several days old, and that we do not know the rate of BA.2 in people tested positive. today or even yesterday.

And, as Olivier Véran pointed out, “the Omicron experience has shown us that 60 cases can be thousands of cases a few days or weeks later”.

The Danish research institute Statens Serum Institut thus relates in an article dated January 20 the rapid progression of BA.2: “The BA.2 subvariant accounted for 20% of all Covid-19 cases in Denmark during week 52 [du 27 décembre au 2 janvier]“, and 45% in week 2, that is from January 10 to 16. Its proportion in the number of infections has since exceeded 50%.

Dangerousness and contagiousness under study

“The preliminary indicators show that there is no difference between BA.1 and BA.2 for hospitalizations, that it is not more virulent”, explains to BFMTV Troels Lillebaek, director epidemiologist at the Statens Serum Institut. , “on the other hand BA.2 seems to be transmitted more easily and this is a problem in itself”.

Indeed, even if contamination leads to fewer hospitalizations, mechanically, the more infections there are, the more the number of patients increases.

BA.2 is therefore currently under study. And if it seems a priori more contagious, “the whole question is to know what will be its seriousness”, notes Jean-François Delfraissy. He explains that this subvariant “is mutated in a different way in the Spike protein, which is the protein that allows the virus to attach to its receptor, but which is also the target of the vaccine response and the monoclonal antibodies with which we can treat these patients.”

These mutations could therefore modify the properties of the virus at different levels, “for example with regard to the infectivity, the effectiveness or the severity of the vaccine”, notes the Statens Serum Institut. But the body adds that “so far there is no information as to whether BA.1 and BA.2 have different properties”.

Olivier Véran raised on Tuesday the possibility “that we could potentially recontaminate ourselves with BA.2, even when we would have been contaminated with the Omicron variant”, stressing however that we did not have “conclusions at this stage”.

“It’s more of a theoretical possibility because of the quite large differences between BA.1 and BA.2, but so far I haven’t seen any data” on this subject, says Troels Lillebaek.

What is its role in the current wave?

Due to the small number of cases detected at the moment, it can be said that BA.2 is not the cause of the current fifth wave in France, in which BA.1 is still very much in the majority. On the other hand, it is possible that its appearance is one of the many reasons why the decline expected in mid-January did not take place.

It is a “possible element of this small increase in the figures”, explained Tuesday on BFMTV our health consultant Alain Ducardonnet.

“We were hoping to reach the peak in January but now we are expecting more February” and therefore “it could be a little later in France too”, also says Troels Lillebaek. Jean-François Delfraissy sees, according to the latest data, this fifth wave landing “rather towards mid-March with a very slow gradual decline in terms of hospitalizations, and a number of contaminations which will slowly end up decreasing”.

Salome Vincendon BFMTV journalist