Less than 10% of the population has been infected by the coronavirus in Ile-de-France and in the Grand Est, the two regions most affected in France. This is what reveals a study published Wednesday which estimates at 4.4% the figure at the national level. At the end of April, the Institut Pasteur had published the first estimates of the contamination of the French population, predicting that 5.7% (margin of uncertainty between 3 and 10%), or 3.7 million people, would have been contaminated with May 11.
Uncertainty intervals "between 3 and 7%"
In the updated results of this modeling, published Wednesday in the journal Science , the percentage is revised down slightly, to 4.4% (with a margin of uncertainty between 2.8 to 7.2), or 2, 8 million people as of May 11.
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"It is above all the intervals of uncertainty that count: we were between 3 and 10%, today we are between 3 and 7%. On a purely epidemiological level this variation does not change anything, we remain in the same order of magnitude "said Simon Cauchemez of the Institut Pasteur.
In all cases, the figure is very far from a level sufficient to achieve collective immunity making it possible to avoid a second wave without measures to control the epidemic. "It would take about 65% of the population to be immunized for the epidemic to be controlled by immunity alone," write the authors.
A resumption of the "probable" epidemic
"Our results therefore strongly suggest that, without a vaccine, group immunity alone will be insufficient to avoid a second wave at the end of confinement," they insist. "Effective control measures to limit the risk of transmission must be maintained beyond May 11 to avoid a rebound in the epidemic." "We are waiting for more serological data to be able to better calibrate our models and refine our assessments," said Simon Cauchemez.
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But while the containment is gradually being lifted, "all the available data, all the published studies suggest that a resumption of the epidemic is probable in the absence of control measures", he insisted.
The researchers also looked at the situation in the two regions most affected by the epidemic. According to their estimates, 9.9% (margin of 6.6 to 15.7%) of the inhabitants of Île-de-France would have been contaminated on May 11 and 9.1% (margin 6.0 to 14.6% ) in the Great East.