Olivier Véran indicated as early as January 25: after being infected for the first time by Omicron, or rather by its BA.1 sub-lineage, "we could potentially recontaminate ourselves" with its "little brother" BA.2.
A Danish study, published on Tuesday, confirms this.
“Infection with two different sublineages of Omicron is possible,” but “this seems to occur relatively rarely in Denmark,” says the Statens Serum Institut.
Let's resume.
BA.1 and BA.2 are therefore two “cousin” variants within the Omicron family.
They are distinguished by their genomic code, with many mutations in common but also some specific to one and the other.
BA.1 (with its own sub-lineage BA.1.1) is still largely in the majority in France, but BA.2 represents an increasingly large share of positive cases there (15% in the last survey of February 7).
It is even already a large majority in Denmark.
It is therefore from this country that the first data on the risk of reinfection by one then by the other of these two sub-lineages of the Omicron variant were expected.
“First study” documenting reinfections
A group of 1.8 million inhabitants who tested positive from November 22, 2021 to February 11, 2022 were followed.
67 cases of reinfection, that is to say two contaminations by Omicron during a period of between 20 and 60 days, have been identified.
Among them, 47 corresponded to people who caught BA.1 then BA.2.
“These Omicron BA.2 reinfections occur shortly after BA.1 infections, but they are rare,” conclude the authors, whose work has not yet been peer-reviewed.
This is “the first study” documenting such a finding, they add.
In detail, these reinfected people were mostly unvaccinated young people.
They only suffered from fairly mild symptoms, which suggests less severity for both BA.1 and BA.2 compared to the Delta variant.
“We can also find people who simply have specificities in the immune system, so these are very specific situations”, points out Etienne Simon-Lorière, head of the evolutionary genomics unit for RNA viruses at the Institut Pasteur. .
Still insufficient data on antibodies
The British health agency had published, on February 11, other data for the United Kingdom.
69 positive cases seemed to correspond to a reinfection, maximum 90 days after the first contamination: 28 between 28 and 59 days and 41 between 60 and 89 days.
But when information was available, namely on 51 of these 69 cases, “none was compatible with a BA.1 infection followed by a BA.2 infection”.
Read alsoOmicron: why the BA.2 sub-variant should not restart the Covid epidemic (for the moment)
In its latest projections, which go until April 1 only, a modeling team from the Institut Pasteur also makes “the hypothesis that people infected with an Omicron virus are immune to Omicron reinfections”.
“But we don't yet have a lot of data on the potency and persistence of antibodies after infection with BA.1,” delays Etienne Simon-Lorière, who expects to see things more clearly in the weeks to come.
