Covid-19: why have some people never caught it?



When Fabienne’s son catches Covid at school at the end of October 2021, she resigns herself, ready to be infected in turn: “He is 9 years old, we were not going to isolate him or prevent him from giving us a kiss”, she explains. A few days later, her husband, vaccinated with two doses like her, tested positive. But Fabienne and her 12-year-old daughter, nothing. Since then, she has still not caught the virus.

→ INVESTIGATION. Covid-19: “Test, trace, isolate”, a strategy undermined by Omicron

While some are particularly cautious and have greatly reduced their social interactions to avoid being contaminated, others like Fabienne remain vigilant but to a lesser extent: “I’m careful but I still go shopping, I take public transport, I see people… I’m no less exposed than the others! », she wonders.

Beyond the most cautious and asymptomatic who do not know they have had the virus, various scientific factors could explain why some people would be less likely to catch Covid, despite the record number of contaminations generated by the Omicron wave.

The flu, a bulwark against the Covid?

Already, people who have been sick with Covid-19 are protected by the antibodies produced by the body to defend themselves against the virus. This is not what protected Fabienne: “I did a serological test and I had no antibodies,” she says. But Covid-19 is not the only disease that could affect immunity.

Thus, having had the flu could constitute a form of protection. “Some people may be in an immunological state that does not favor infection: if there has been a flu recently for example”, explains Olivier Schwartz, director of the virus and immunity unit at the Institut Pasteur. The body is then in an antiviral state “with molecules that could constitute a form of protection against the virus”, advances the professor. According to a study conducted by researchers at Imperial College London, the common cold could also have a protective role.

The role of genetics and blood type

Genes could also be a natural resistance factor to the virus. In some people, the receptors to which the Covid virus clings to infect its host would be slightly different: “You sometimes find a rare gene variant of the ACE2 receptor. » A rare genetic specificity “which could induce some form of protection against Covid-19”, reports Olivier Schwartz.

“There are also some people with inflammatory or autoimmune diseases who have an interferon mutation”, he adds, a molecule produced in reaction to the virus and which reduces viral multiplication. This mutation would place these people “in an antiviral state” which would thus make them more resistant to contamination.

→ THE FACTS. Omicron wave: the epidemic peak is long overdue

Another hypothesis is that of blood group: people with group O may have less chance of being infected. “In reality, the effect is relatively small, warns Olivier Schwartz, there is less than 10% reduction in susceptibility to infection” for these people.Fabienne is not from group O but she still fell through the cracks. “It’s luck”, she concedes.

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