A screening “insufficient“. This is what Inserm researchers denounce. They publish in the journal Nature an article which points to a failure of the surveillance system at the exit of the first containment.

These researchers used a mathematical model to draw the first scientific lessons from the “test – trace – isolate” device set up in early summer 2020.

Read also: PCR, saliva, antigen, we help you sort out the different covid tests

Multiple data

They used several data: hospital admission figures region by region, socio-demographic data, estimates from Public Health France indicating the percentage of people complying with barrier gestures or even mobility data from Google.

They also took into account data from the participatory virus surveillance site. Covidnet.fr and data from the national virological surveillance system SI-DEP which records all the results of covid tests performed by the laboratories.

90,000 unidentified symptomatic cases

Result: from their models and the data collected, the scientists note that the number of symptomatic cases has been largely underestimated.

Thus, nearly 104,000 symptomatic infections occurred between May 11 and June 28, 2020, against just over 14,000 officially recorded cases. That is to say 90,000 unidentified symptomatic cases over this period.

In other words, nine out of ten symptomatic cases were not detected after the end of the first national lockdown in May.

Not enough screening, even when the virus was circulating little

Another finding: only five of the 12 regions studied exceeded a median detection rate of 50% at the end of June and less than a third (31%) of people with covid-19-type symptoms consulted a doctor despite the recommendations.

The screening capacity “remained insufficient, even at the low levels of viral circulation reached after this confinement“and it was predictable that she”deteriorates rapidly with increasing epidemic activity“, note the authors of the study.

Only one infection in 12

Worse, if the researchers include asymptomatic cases, that is to say without symptoms, in their calculation, “only one in twelve SARS-CoV-2 infections was identified during the study period“seven weeks after lockdown,” said Jeffrey Shaman of the Mailman School of Public Health at Columbia University (New York) in a commentary also published in Nature.

The majority of SARS-CoV-2 infections were therefore not detected during the first weeks after this confinement, interpret the authors of the article.

“Major obstacle to the control of the epidemic”

Gold “a strong underestimation of cases is a major obstacle to controlling the epidemic ” recalls Vittoria Colizza, co-author of the study, in a Inserm press release.

“Test-trace-isolate is the only way we have to continue to slow the spread of the virus by easing restrictive measures targeting the entire population“continues the specialist in infectious disease modeling.

Today, “the task is all the more difficult since we are in the winter period“she admits, before concluding:”We must continue to strengthen screening capacities so that they are more targeted, effective and accessible to all in order to fight the pandemic“and avoid a third wave.