Should we fear a new wave of Covid-19 contamination? This is the question that the Institut Pasteur has tried to answer. According to one study published Thursday, March 10 (PDF)experts believe that “in all scenarios explored, the peak of cases (in March) remains well below the January peak.”
According to the previous report by the Institut Pasteur, published on February 21 (PDF)BA.2, a sub-variant of Omicron, should not on its own cause any “significant rebound in the epidemic”. This rebound was “possible”according to the models, “if the French relaxed their behavior”. However, as of Monday, March 14, many restrictions will be lifted. The mask will no longer be compulsory at school. The health protocol will no longer be applied in business. Finally, the vaccination pass will no longer be required, as well as the mask in stores.
While for a week, the number of contaminations has been rising slightly, after a period of decline since the peak of the last wave, at the end of January, and Olivier Véran, on Friday March 11, reported a tremor of the pandemic, Franceinfo takes stock of the results of these new models.
The unsurprising progression of the Omicron BA.2 sub-variant
“Our model correctly predicted the dynamics of the BA.2 proportion among Omicron cases, notes the Pasteur Institute. The model anticipated that 29% and 45% of Omicron cases would be BA.2 on February 14 and 21; flash data available March 9 indicates 25% and 40% BA.2 cases among Omicron cases on those dates.”
>> Covid-19: what we know about the Omicron BA.2 sub-variant detected in France
During the last week of February, the BA.2 subvariant indeed represented 43% of new positive cases for the coronavirus, according to Public Health France (PDF). According to preliminary data from this same epidemiological point, it should nevertheless become the majority from the first week of March (52% of new contaminations).
Contamination plateau reached earlier than expected
According to the February models, the Institut Pasteur was “the hypothesis that the French would increase their contacts from March 1, leading to a plateau of contaminations in early March”. Corn “the plateau in contaminations was observed slightly earlier, suggesting that these changes took place before March 1st”.
The French would therefore have had more contacts from the end of February. The curve of Covid-19 infections is close “projections obtained under the assumption that from February 22, the French increased their contacts by about 40% compared to January-February levels”. This additional level of contact intensity, +40%, is “slightly higher than that measured in December 2021”or “transmission rates (…) were roughly 30% higher than January-February transmission rates”.
Transmission rates of up to 130% after restrictions are lifted
In this study, the Institut Pasteur starts from hypotheses of high transmission rates. In effect, “The relaxation of control measures on March 14 should further push up transmission rates”, reports the Institute.
The scenarios are therefore based on transmission rates “50%, 70%, 100% or 130% above January-February levels.” For comparison, November 2021 contact rates were “about 60-70% higher” to those of early 2022 and those of December, 30% higher.
In March, a peak in cases “much lower” than in January
Two scenarios were modeled by the Institut Pasteur. The first explores the hypothesis of a relaxation of measures – and therefore of an increase in contacts – March 14. Corn “in practice”, “the French could anticipate the relaxation of the measures” barriers and have more contacts before March 14. A second scenario is therefore based on a change in habits a week before, from March 7.
“In all the scenarios explored, the peak of cases remains much lower than the January peak, concludes the Institute. It could exceed 100,000 daily cases in March in scenarios where transmission rates increase very significantly following the relaxation of control measures. This would be higher than the current figures but significantly lower than the figures seen during the last wave at the end of January.
Indeed, 58,336 positive cases were counted daily on average over the week preceding March 10. The shift is already observable, with 74,818 positive cases on Thursday March 10 alone.
But this remains far from the height of the epidemic wave at the start of the year, when 501,635 new infections were observed on January 25. The Institut Pasteur’s projections for March are therefore five times lower than the contamination record observed since the start of the pandemic.
Projections potentially “too optimistic”
Nevertheless, in the preamble to the study, the Institut Pasteur calls for these encouraging results to be taken with caution, which rule out the possibility of a new epidemic wave from March.
This study did not include “the progressive decline of immunity, which could make” projections “too optimistic”. Likewise, “climate impact” was not taken into account for these models.