What to remember from Institut Pasteur’s latest reassuring models

Should we fear a new wave of Covid-19 contamination? This is the question the Pasteur Institute is trying to answer. according to someone Study published Thursday, March 10 (PDF)experts believe “In all investigated scenarios, the peak of cases (in March) It remains well below its January peak”.

According to a previous report by the Pasteur Institute published on Feb. (PDF)BA.2, a sub-variant of Omicron, for whatever reason on its own “a significant recovery in the epidemic”. That’s the kickback “possible”According to the models, “If the French relax their behavior”. However, from Monday, March 14, many restrictions will be lifted. Masks will no longer be required in schools. The health protocol will no longer be applied in business life. Finally, the vaccination card will no longer be required, as well as the mask in the stores.

After a period of decline since the peak of the last wave at the end of January, while the number of contaminations increased slightly over the course of a week, Olivier Véran reported a tremor in the pandemic on Friday, March 11, Franceinfo evaluates the results of these new models.

Unsurprising progression of the Omicron BA.2 subvariant

“Our model accurately predicted the dynamics of the BA.2 ratio among Omicron cases, Notes the Pasteur Institute. The model predicted that 29% and 45% of Omicron cases on February 14 and 21 would be BA.2; Available flash data as of March 9 show 25% and 40% BA.2 cases among Omicron cases on those dates.”

>> Covid-19: What we know about the Omicron BA.2 subvariant detected in France

According to Public Health France, in the last week of February the BA.2 subvariant indeed represented 43% of new positive cases for coronavirus. (PDF). According to preliminary data from the same epidemiological point, it should nevertheless become the majority by the first week of March (52% of new contaminations).

Contamination plateau reached earlier than expected

According to February models, Institut Pasteur “The hypothesis that the French will increase their contacts from 1 March, leading to a contamination plateau at the beginning of March”. sweetcorn “The plateau in contaminations was observed a little earlier, suggesting that these changes occurred before March 1”.

Therefore, the French would have more contact 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 density, +40%, “Slightly higher than measured in December 2021”or “transmission rates (…) were about 30% higher than January-February transmission rates”.

Up to 130% delivery rates after restrictions are lifted

In this study, Institut Pasteur starts off from high transfer rates hypotheses. In the effect, “The relaxation of control measures on March 14 should push transmission rates even higher” Notifies the institute.

The scenarios are therefore based on transmission rates. 50%, 70%, 100% or 130% above January-February levels.” For comparison, contact rates for November 2021: “about 60-70% higher” 30% higher for early 2022 and December.

A “much lower” peak in cases in March than in January

Two scenarios were modeled by the Institut Pasteur. The first explores the hypothesis of a relaxation of measures and thus an increase in contacts. 14 March. sweetcorn “in practice”, “The French can wait for the relaxation of measures” There are obstacles and more contacts before 14 March. So a second scenario is based on a change in habits a week before March 7.

“In all the scenarios investigated, the peak of cases remains much lower than the January peak, He finishes the institute. In scenarios where transmission rates increase dramatically following the relaxation of control measures, it could exceed 100,000 daily cases in March. This will be higher than current figures, but significantly lower than those seen in the last wave at the end of January.

Indeed, an average of 58,336 positive cases per day were counted during the week before 10 March. With 74,818 positive cases on Thursday, March 10 alone, change is already observable.

But this is far from the height of the epidemic wave at the beginning of the year, when 501,635 new infections were observed on January 25. That’s why the Pasteur Institute’s estimates for March are five times lower than the contamination record observed since the start of the pandemic.

Forecasts potentially “too optimistic”

However, the Pasteur Institute calls for caution at the study’s introduction to these encouraging results, which rule out the possibility of a new wave of epidemics starting in March.

This study was not included “Progressive decline of immunity that can” projections “too optimistic”. Same way, “climate effect” These models are not considered.