Why, since the start of the pandemic, have some people stubbornly resisted infection with SARS-CoV-2 while so many others, faced with the same risk situations, were quickly infected? Since the start of the pandemic, the question has fascinated as much as it intrigued. The enigma, however, also appears tough than the subjects to which it devotes itself. Genetic mutations, past encounters with other viruses, blood type, lifestyles…: many are the avenues explored. Already, some are taking shape with greater clarity.
Who are these resistant to the virus? “The typical example is that of close intra-family exposures. In a couple, for example, one of the two partners can be affected without always knowing it: it happens that his spouse remains unscathed., says Professor Laurent Abel, co-director of the human genetics of infectious diseases laboratory at the Imagine Institute (Inserm, Necker Hospital, Paris). Not to mention those who, despite a risky profession, have always passed between virus-laden drops, droplets and aerosols, even when masks were not available.
We still have to agree on this natural protection. There are people who resist infection with SARS-CoV-2 despite obvious exposure to risk and in the absence of vaccination. And then there are those who are infected but do not develop serious forms of Covid-19. These two categories of resistance, a priori, are due to different shields. Only the first concerns us here.
Near-perfect shield
“The proportion of humans naturally resistant to SARS-CoV-2 infection is unknown”note the authors – an international consortium, including Laurent Abel – of a state of the art on the subject, published in October 2021 in the journal Nature Immunology. But, as far as the genetic trail is concerned, “ a number of candidate genes […] have been proposed “, they add.
Before that, the researchers had to meet a first challenge: how to be sure not to miss an asymptomatic infection? “The absence of infection must be established by repeated negative PCR tests, then confirmed by negative serology”, emphasizes Laurent Abel. If an individual’s blood does not contain antibodies targeting SARS-CoV-2, it is because their immune defenses have not encountered the virus. With a caveat: “When the mucous membranes of the nose are infected, local immunity may be sufficient to block infection from the rest of the body. No antibodies will then be detected in the blood.underlines Jean-Daniel Lelièvre, head of the clinical immunology and infectious diseases department at the Henri-Mondor hospital in Créteil (AP-HP).
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