the BA.2 variant unlikely to cause an epidemic rebound according to the Institut Pasteur

“The BA.2 epidemic is slowing the decline in cases without however generating a significant epidemic rebound”, writes the research institute in its models, which run until April 1.

If the BA.2 variant continues to spread in France, it should not cause an epidemic rebound, at least until April 1, explains the Institut Pasteur in its latest models published this week. He writes that “the BA.2 epidemic is slowing down the decrease in cases without, however, generating a significant epidemic rebound.”

The Institute thus explains that while “non-BA.2 Omicron cases are decreasing significantly, BA.2 cases continued to increase at the end of January-beginning of February. Under these conditions, it is expected that 50% of Omicron cases are BA.2 infections around February 24”.

Number of infections in thousands (graph C) and number of cases (D) of Covid-19 according to the variants
Number of infections in thousands (graph C) and number of cases (D) of Covid-19 according to the variants © Institut Pasteur

The Minister of Health Olivier Véran also declared on Tuesday that with current scientific knowledge, “we consider that there is no risk that there will be an epidemic rebound of BA.2” in France, even if this sub-lineage of Omicron represents close to 50% of the contaminations currently.

“An epidemic rebound is possible but the scale of this rebound remains very limited”

These projections are made using a baseline scenario: BA.2 is 70% more transmissible than non-BA.2 Omicron viruses, 50% of SARS-CoV-2 infections are detected by the surveillance system, people infected with BA.1 are immune to BA.2, and the latter variant does not escape vaccine protection any more than non-BA.2 viruses. In addition, current behaviors affecting transmission rate remain unchanged.

According to this scenario “the peak of BA.2 cases could occur in mid-February and remain modest in size” with an average of 24,000 contaminations per day (between 7,000 and 54,000). Other less favorable scenarios have been studied, but the curve of infections due to BA.2 varies little. “An epidemic rebound is possible but the scale of this rebound remains very limited”, explains the Institut Pasteur.

Potential evolutions of the Covid-19 epidemic curve according to an increase in transmission rates
Potential evolutions of the Covid-19 epidemic curve according to an increase in transmission rates © Institut Pasteur

This could be due to immunity acquired through vaccination or natural contamination it is explained, because “given this significant immunity, it is not expected that the BA.2 subvariant can generate a rebound height of the epidemic in the short term, even if this variant is more transmissible than non-BA.2 Omicron viruses”.

“No difference in terms of severity between BA.1 and BA.2”

These results are projections based on criteria that may change over time, which would modify the models. The Institut Pasteur thus recalls not having modeled “the gradual decline of immunity, which could make our projections too optimistic”. On the other hand, “our projections could be less favorable if, in addition to being more transmissible, BA.2 evaded immunity more than non-BA.2 Omicron viruses.”

According to the latest conclusions of the World Health Organization, BA.2 does not in any case show an increased virulence compared to BA.1. “We do not see a difference in terms of severity between BA.1 and BA.2 and therefore it is a similar level of severity in terms of the risk of hospitalization,” said Maria Van Kerkhove, who oversees the fight, on Tuesday. against Covid-19 at the WHO.

Salome Vincendon

Salome Vincendon BFMTV journalist

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