During the weekend, the list of the first serological tests approved by the National Reference Center (CNR) for respiratory infection viruses was sent to the Directorate General of Health. The first specific list is expected to be released this week. At the end of March, the French government had placed an initial order for a serological test with the American group Abbott, to find out by blood sample if a person infected with the virus developed an immune response. In the United States, 3 serological tests from the American group have been authorized. In addition, in France, other companies are in the running, such as BioMérieux, Roche or NG Biotech.
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The performance of future commercial serological tests has been compared with that of the best laboratory tests designed by the Pasteur Institute. More than 100 serological tests have been recorded worldwide, estimates the NGO Find, specialized in diagnostics, about fifty of which have received a "CE marking". This European label says nothing about the effectiveness of the test: it is a "self-certification" of the manufacturer, without verification of performance. The High Authority for Health (HAS) has therefore added criteria: specificity greater than 98% and sensitivity of at least 90%.
The specificity indicates that the test applies well to SARS-CoV-2 and not to the six other known coronaviruses, some of which cause simple colds; otherwise there would be too high a risk of "false positives", people wrongly detected. Sensitivity determines the number of people infected with SARS-CoV-2, even with a low presence of antibodies in the blood: a way to limit "false negatives", infected people who ignore each other. According to HAS criteria, one in 10 results could be wrong. Serological tests will therefore mainly be used for epidemiological studies and to diagnose healthcare personnel. They will also be used to monitor cured patients who had developed Covid-19 and to refine diagnoses, as in the case of a virological test (PCR) with questionable results.
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New York State has just started testing its hospital staff. But faced with possible misses, the World Health Organization (WHO) reminded countries on Saturday of great caution in the preparation of "immunity passports" . Serological tests are not perfect, "the use of these certificates can therefore increase the risk of continued transmission," warns WHO.
