Health Serological tests, between the race for reliability and...

[Innover contre le virus] Serological tests, between the race for reliability and the search for immunity

During summer, Industry & Technologies looks back on several months of mobilization of industrialists and researchers to face the Covid-19 pandemic. Today, the development of serological tests, allied with molecular screening by RT-PCR. By detecting antibodies developed more than a week after infection with SARS-CoV-2, they can potentially indicate whether an individual has developed immunity to the virus.

Complementary tests to RT-PCR screening

Besides molecular tests by RT-PCR, other types of tests were eagerly awaited to provide new information on the epidemic. The development of serological tests, which detect the presence in serum or blood plasma of the antibodies that an individual has developed against the disease, is being closely monitored. Complementary to RT-PCR, they can potentially indicate whether a part of the population is immune. At the end of March, however, these tests were far from ready. Olivier Véran, Minister of Health counted at the time on research to obtain them “within a few weeks”.

The Pasteur Institute in action

Several teams from the Institut Pasteur, CNRS, Inserm and the University of Paris, were working on four serological tests capable of detecting the presence of antibodies: ELISA N, ELISA S (each targeting the antibodies generated by two distinct proteins of the virus), S-Flow (requiring a flow cytometer) and the more versatile LIPS tests called immunoprecipitation.

Master the sensitivity and specificity

At the beginning of April, several manufacturers entered the race and sought to develop the test with the best sensitivity (detection of antibodies, even in small quantities) and the best specificity (detection only of antibodies characteristic of covid-19).

NG Biotech, the first to unveil its test

The Breton company NG Biotech, which relied on a chinese technology to speed up the development of its test, launched at the end of March the production of a device capable of detecting IgM (immunoglobulin M) and IgG (immunoglobulin G) produced by the body in 15 minutes. These rapid tests, in the TROD category (rapid diagnostic orientation test) make a first diagnosis from a drop of blood. If the test shows a specificity of 100%, without a false positive, its sensitivity only reaches 70% 10 days after the onset of symptoms.

Roche seduces across the Atlantic

For its part, Roche, a Swiss pharmaceutical laboratory, received, on May 3, an emergency use authorization (EUA) from the Food and Drug Administration (FDA), the federal drug authority in the United States, for its Elecsys Anti-SARS-CoV-2 test. Proven in 5,272 patients, it claims a specificity of 99.8% for a sensitivity of 100%. The sensitivity rate was verified by testing the patients 14 days after confirmation of their infection with SARS-CoV-2.

BioRad relies on French know-how

74 days, instead of 18 months. The American Bio-Rad has developed in record time its serological test to detect whether a patient has developed specific antibodies in contact with SARS-CoV-2. It displays high performance: 100% sensitivity after 8 days, and 99.6% specificity. The company drew on its knowledge of coronaviruses and its previous work carried out with the Institut Pasteur.

Focus on immunity research

A subfamily of serological tests, called sero-neutralization tests, aim to determine whether the antibodies produced by a patient provide long-lasting protection against the virus. These tests aim to detect specific antibodies, called neutralizers, which block the interaction between the virus and the cells of the body. These tests have been developed at the Institut Pasteur from chimeric viral particles incorporating virus target proteins.

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