Less than 10% of the infected population in the two most affected French regions

Less than 10% of the population has been infected with the new coronavirus in Île-de-France and the Grand Est, the two regions most affected in France, according to a study published Wednesday which estimated the figure at 4.4% 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.

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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. “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, ”explained Simon Cauchemez, of the Pasteur Institute, to AFP.

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 Ile-de-France would have been contaminated on May 11 and 9.1% (margin 6.0 to 14.6% ) in the Great East.

No collective immunity

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.

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"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 so that we can better calibrate our models and refine our assessments," said Simon Cauchemez.

“Probable” recovery without control measures

But while the containment is gradually being lifted, "all the available data and all the published studies suggest that a resumption of the epidemic is likely in the absence of control measures", he insisted.

The small share of the infected population is due to confinement itself, notes the study, according to which the average number of people infected by a case rose from 2.9 at the national level before confinement to 0.67 at the end.

The study also estimates that 3.6% of those infected were hospitalized and 0.7% died with very significant differences according to age (from 0.001% for those under 20 to 10.1% for over 80s).