What the first serological study on Covid-19 by the Institut Pasteur says

An epidemiological and serological study by the Pasteur Institute, unveiled this Thursday morning, allows us to better understand the development of the Covid-19 epidemic in the Oise in March but also to see what slowed it down. Nicotine also appears to reduce the risk of infection.

It is the very first sero-epidemiological study in France. A team from the Institut Pasteur looked into the development of Covid-19 infection in a high school in Crépy-en-Valois (Oise). The work was carried out from March 30 to April 4 in one of the main epicentres of the development of the virus in France, with high school students and their respective contacts. The study began a little over a month later the death of a Crépy teacher, February 25, first case reported without direct link to China.

This epidemiological and serological study (therefore looking for antibodies), conducted by a team of Professor Arnaud Fontanet, with the support of the Hauts-de-France Regional Health Agency, the Académie d ‘Amiens and the French Blood Establishment was intended toaccurately determine the share of people affected by Covid-19. It makes it possible to draw a lot of lessons on the development of the epidemic in a population basin like the commune of Île-de-France.

School holidays, a brake on the epidemic

The first of its kind, the study was conducted with 661 people, high school students and their contacts (teachers, families). Thanks to virus detection tests associated with serological tests developed by the Institut Pasteur, this study reveals that 26% of the study population was infected with SARS-CoV-2 and has antibodies against this virus. The proportion is higher among high school students themselves and their teachers: 38% of infected high school students, 43% of teachers.

“The virus has circulated a lot in the high school and the closure for the school holidays had a very strong impact: the transmission stopped and the confinement on March 1 in Crépy ended the epidemic”, underlines Arnaud Fontanet, head of the “epidemiology of emerging diseases” unit at the Institut Pasteur.

In the families of high school students, the contamination was lower (around 10%). It also appears that 17% of people who developed antibodies had no symptoms.

However, “The attack rates observed among study participants suggest that collective immunity will not be established quickly. In addition, other regions of France, where the virus has not yet circulated, are almost naive compared to this virus “, adds Arnaud Fontanet.

Nicotine, a treatment avenue?

The study also confirms that loss of smell and taste are the two symptoms that have a very strong predictive value in favor of an infection.

But another interesting lesson, which comes on top of observations in progress and which France Inter revealed to you, smokers are less sick than others.

In fact, 7% of smokers were infected while four times more of non-smokers were infected. “This corresponds to a 75% reduction in the risk of being infected for smokers”, explains Arnaud Fontanet. “Perhaps nicotine could have an effect … It is a line of research for prevention as well as for treatment”, adds the researcher from the Institut Pasteur.

Three reliable tests developed in parallel

With researchers from CNRS and Inserm, scientists from the Institut Pasteur have, in parallel, carried out a study to assess the reliability of several test models, in particular two types of serological tests:

• antibody tests to assess whether a person has developed and therefore has already contracted the virus;
• neutralization tests to determine if a person is immune to the virus using so-called “neutralizing” antibodies.

Used in particular in the Oise, these tests have shown great reliability and could be developed on a larger scale.

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