More than 3.6 million people tested positive in France in almost a year, but how many inhabitants have actually been infected with SARS-CoV-2?
The Institut Pasteur unveiled on Wednesday, on a new section of its site presenting its models, a very latest estimate of the adult population having been contaminated.
As of February 16, it is estimated that around 17% of people over 20 living in metropolitan France have been affected, or around 8.5 million people.
To arrive at this figure, the Institut Pasteur based itself on the number of people hospitalized as well as on "an estimate of the probabilities of being hospitalized when one is infected", calculated during a seroprevalence survey during the first period. wave.
Here is what to remember, in detail.
The Île-de-France by far the most affected
The region was one of the most affected by the epidemic during the first wave as during the second, the latter having not yet receded much.
It is therefore logically in Île-de-France that the proportion of the adult population having been infected is the highest (around 30%), according to the latest estimates from the Institut Pasteur.
Provence Alpes Côte d'Azur comes in second (around 23%) whereas it was only third last October.
This increase is not illogical since several departments located on the Côte d'Azur, including the Alpes-Maritimes and the Bouches-du-Rhône, have been severely affected in recent weeks.
The Grand-Est is downgraded by one place and this time is third.
Conversely, Brittany confirms its status as a relatively untouched territory.
Less than 6% of adults who live in one of the four Breton departments have been infected in nearly a year.
It is still in this region that the incidence rate (that is to say the number of people infected over seven days per 100,000 inhabitants) is the lowest, even if it is now over 100.
Almost a quarter of those under 50 infected
At 20 or 30, we often have more social and human contact than older people.
This is undoubtedly one of the reasons why the youngest adults appear to be more affected than the others.
In each of the age categories under 50, a little less than 25% of French people have been infected since March 2020. Warning: the margin of uncertainty is significant for 20-29 year olds, from 15 to 35 %.
Conversely, just over 10% of 60-69 year olds or 70 year olds have been in contact with the virus.
This pattern in which those under 50 are more affected also appears at the level of each of the metropolitan regions.
Estimates to be qualified
As the Institut Pasteur itself specifies, the method used to arrive at these estimates has limitations.
On the one hand, it is based on the assumption that “the probability of being hospitalized when infected has remained constant in each age group”.
This may not be the case if a treatment is effective, for example.
"It is possible that these probabilities have varied during the pandemic or from one region to another", recognizes the organization.
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The rate of 17% also confirms that we remain very far from collective immunity, reached when at least half of the population has been infected.
In any case, having already been infected does not necessarily mean that you are immune over time.
The Haute Autorité de santé even recommends that these people be vaccinated at least three months after the onset of symptoms, but with a single dose and not two.
This would indeed be enough to provoke a sufficiently protective immune response, according to several scientific studies.