Paris (AFP)
An epidemiological study in a high school in Crépy-en-Valois in the Oise, in an epicenter of the Covid-19 epidemic in France, reveals that 26% of teachers, high school students and their families have been infected and have antibodies against the virus, according to the Pasteur Institute.
A level completely insufficient to justify the slightest relaxation, according to the researchers.
In detail, 41% of high school students, teachers and staff working in this school were infected with the new coronavirus during an epidemic in February-March, according to this study published Thursday, carried out using detection tests for antibody.
But only 11% of the relatives of high school students (parents and siblings) had antibodies against SARS-CoV-2.
This is far from the 60% to 70% hoped for in the general population to have sufficient group immunity to stop the epidemic, provided that the antibodies are really protective against the coronavirus and that this immunity lasts at least several months.
"We are not sure about the protective nature of antibodies", underlines Pr Arnaud Fontanet, first author of the study and head of the Epidemiology of emerging diseases unit at the Institut Pasteur in Paris.
In the case of the SARS epidemic that started in China in the early 2000s, studies had reported that 10% of patients had no more antibodies after 12 months.
- "Positive effects" of containment -
The results of this study suggest that collective immunity will not be established quickly. Especially since "other regions of France are almost free" from contact with this virus, adds the researcher.
He notes, however, "the positive effects of confinement on the slowdown of the epidemic: the February school holidays and confinement in the Oise (intervened on March 1, before its extension to the country on March 17) have greatly reduced traffic virus in the weeks that followed. "
The study, posted online on the MedRxiv site, was carried out from March 30 to April 3 in a high school in Crépy-en-Valois (Oise) linked to a cluster of infection cases ("cluster").
It tested 661 people - high school students, teachers, staff working in the establishment, as well as parents and brothers and sisters of high school students. A total of 171 (25.9%) people tested positive for serology from a blood test.
The infection rate is similar in both sexes.
Intra-family contaminations do not appear so frequent: the risk of being infected within the home increased from 9% to 17% for parents if the student was infected, and from 3% to 21% for siblings if the high school student was infected.
The 9% of parents infected when the high school student was not given an estimate of the circulation of the virus in the adult population in Crépy-en-Valois.
The rate was only 3% in infected blood donors in two nearby blood banks.
- Loss of smell -
5.3% of those infected were hospitalized (aged 49 years on average compared to 18 years among those not hospitalized) and there were no deaths. "High school students are closer to adults for the capacity to transmit the virus than to children," says Professor Fontanet.
Three serological tests developed by the Institut Pasteur, "very effective", with "less than 1% false positives" were used, underlines Bruno Hoen, co-author of the study and director of medical research at the 'Pastor Institute.
"They were previously tested on blood bank samples dating from 2018 and 2019, when the new coronavirus did not circulate in France," said Professor Fontanet.
Among the symptoms, the study confirms that the infection is found in 84.7% and 88.1% of people who have lost their sense of smell and taste.
At least 17% of those infected did not have symptoms.
The infection affected fewer smokers (7.2%) than non-smokers (28%) in this study, confirming previous observations of a very low rate of smokers in patients hospitalized for Covid-19. But "smokers, in the event of contamination, risk making more complications from the Covid-19 disease", warns Professor Fontanet.
© 2020 AFP