why some do not catch the virus even by being exposed to it?

While more than 460,000 contaminations have been recorded in 24 hours and nearly 15 million French people have already contracted Covid-19, some people escape it despite close contact with patients.

This is one of the many mysteries around this disease that is Covid-19. While the virus is transmitted very easily between people who are in close contact with each other, or even by aerosols which can remain in suspension for several minutes, some people seem to be uncontaminable. Since the start of the pandemic, some have caught Covid-19 one, two or even three times, while others, highly exposed to the virus by living for example under the same roof as positives, have never tested positive. . So why ? While there isn’t really a definite answer, scientists have a few guesses.

First, people who have never tested positive may have already contracted the virus asymptomatically and mistakenly think they never had it. But several reasons can explain the fact that some people have never caught it, analyze the doctors.

Unequal in the face of disease

The first is that we are not all equal in the face of the disease and that our immune system does not react in the same way to the virus, as with each disease. The immune response to Covid-19 may therefore be stronger for some than for others.

Asked by France Inter, a head of the emergency department of a hospital in the Paris region explains: “We know that we are unequal in the face of diseases (…) Why do some people infected with HIV declare the disease very quickly, whereas others will live with the virus all their lives without the disease ever breaking out? In medicine, we know, genetic susceptibilities are at work, which we cannot explain.

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“It is believed that some people are born with variants or mutations in one or more genes that are important for SARS-CoV-2, he says. Thanks to these mutations, the virus would not succeed in attaching to human cells”, explains to Radio Canada infectious disease specialist Donald Vinh. Thanks to these mutations, the virus would not succeed in attaching to the human cells of certain people.

An “increasingly recognized” genetic predisposition

Last October, the British scientific journal The Lancet pointed out in an article that “the genetic predisposition of the host to Covid-19 is now increasingly recognized”, and that studies had been carried out on this subject.

Nature magazine, for its part, hypothesized that some people would not have ACE2 receptor functional due to a rare mutation, a receptor that SARS-CoV-2 uses to enter cells. A mechanism already observed in the case of other diseases such as HIV, even if this virus involves other receptors.

Blood type could also play a role. According to one study published in the journal Epidemics, we would have more chances of transmitting the virus to a person of the same blood group and therefore less of transmitting it to someone of the same family who does not have the same rhesus, which could explain why an exposed person of the same way to the virus that another person in his family is not infected. As of 2020, several studies taken seriously by Inserm demonstrated that belonging to group O would reduce the risk of infection and serious forms, in particular compared to those of group A.

A recent study by researchers at Imperial College London published in Nature Immunology shows that people previously infected with other viruses such as colds or flu are less vulnerable to Covid and its variants thanks to T cells developed by the body: “T lymphocytes created by the body when it is infected with d other coronaviruses, such as the common cold, can protect against Covid-19 infection. […] Our study provides the clearest evidence to date that T cells induced by cold coronaviruses play a protective role against SARS-CoV-2 infection”, explains Professor Ajit Lalvani, co-author of the study.

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By comparing the data of 52 people living in the same house as a person who tested positive, the researchers found that those who had caught a cold before had a much higher level of T lymphocytes than others and therefore less likely to contract the virus.

But if the theories and studies are numerous, there is no absolute immunity to the virus and everyone can therefore catch it. This is why anyone must continue to take precautions by respecting barrier gestures.

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