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Studies that rely on detecting antibodies in the blood to estimate the proportion of a population that has been infected with the coronavirus are undoubtedly lower than reality, because the antibodies gradually disappear from the body, according to a study released Wednesday by the Centers for Disease Prevention and Control. (CDC) of the United States.
• Read also: All the developments in the COVID-19 pandemic
Decreasing antibody levels don’t necessarily mean people are at risk of reinfection, as other parts of the immune system continue to watch over and intervene after the initial infection. The actual duration of immunity is not yet known.
Antibody studies have become routine in many countries, performed at different scales, with representative samples, entire villages or often from samples in blood banks.
They helped to take the true measure of the epidemic, in addition to diagnostic tests, which are positive only during infection, not after, and which were and remain in many places too rare, and are not usually performed by people without symptoms.
The CDC collected and tested the blood of more than 3,000 healthcare workers in 13 US hospitals from April to June 2020: 194 people (6%) had antibodies to the coronavirus.
About two months later, 156 of them were tested again: in 94% of them, the level of antibodies had decreased. In 28%, the antibody level had dropped below the threshold that usually indicates a past infection.
“These results suggest that serological tests performed at some point undoubtedly underestimate the number of people who have been infected with SARS-CoV-2 in the past and that a negative serological test does not necessarily rule out a past infection,” the authors summarize. study.
The more symptoms the participants had, the higher the antibody level.
The other conclusion of the study is that it is not recommended for individuals to rely on a serological test to determine whether or not they have been infected with the coronavirus in the past.
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