Covid: Why don’t some people get the virus?

“I never caught the Covid”. We are fewer and fewer to utter this sentence. However, some continue to resist. So how do you explain after seven waves that some have never had Sars-CoV-2? The point with Sandrine Sarrazin, Inserm researcher at the Marseille-Luminy Center for Immunology.

To be contaminated or not… Since spring 2020, more than 32 million cases of Covid-19 have been identified in France. A number that reflects only part of reality. For Sandrine Sarrazin, Inserm researcher at the Marseille-Luminy Center for Immunology, “eBetween asymptomatic forms that have gone unnoticed, people who have been infected twice“Not to mention the screening campaigns that began well after the first cases appeared and didn’t count self-testing, even today it is difficult to say with certainty how many people are actually affected by Sars-CoV-2 .

Still, some never developed the disease for 7 consecutive waves. So how to explain it?

  1. Isolated people or who had it without knowing it?

It is hard to imagine that people would not have come into contact with the virus“, notes Sandrine Sarrazin. “But there must still be rare cases of very isolated people, outside the big cities, who never used public transport, who scrupulously respected barrier gestures, who may have escaped the virus… But this is probably not the majority of those who never develop the disease to have .“Another hypothesis,”those who had it but showed no symptoms, or who thought it was a cold or the flu “, and who therefore imagine that they have slipped through the cracks.

  1. A genetic predisposition?

A French team (Inserm/APHP) led by Professor Jean-Laurent Casanova has already shown that genetic and immunological predispositions explain almost 25% of severe forms of Covid-19, without necessarily having to have comorbidities “continues the immunologist. “Conversely, there are undoubtedly people who are genetically better equipped. The same team is also interested in the genes of healthcare professionals who were exposed to Sars-CoV-2 before vaccines or masks were available… and who didn’t develop the disease..”

Other work has already been done on this possible “genetic protection”. Take these scientists from theNewcastle University who found that the HLA-DRB1*04:01 gene is three times more likely to be found in asymptomatic people. This suggests that carriers of this gene have some level of protection. Note, however, that this gene is directly correlated with longitude and latitude. There are clearly more carriers in Northern and Western Europe. This suggests that the European population is more likely to remain asymptomatic…while at risk of spreading the disease to the most vulnerable populations.

  1. cross immunity?

A study recently published in the journal Nature communication showed that exposure to rhinovirus, the most common cause of the common cold, could protect against Sars-CoV-2 infection. In this work, researchers fromImperial College London found that high levels of T cells produced by the body when infected with other human coronaviruses (e.g. the common cold) can protect against Covid-19 infection. “But that’s just a hypothesis”, tempered Sandrine Sarrazin. “Vaccination also produces strong immunity. However, this does not prevent the development of the disease.

  1. The blood type?

Since the beginning of the pandemic, scientists have been interested in the connection between blood type and the risk of contracting the coronavirus. Many scientific publications have found a connection between belonging to group O and protection against the Sars-CoV-2 virus. But Sandrine Sarrazin realizes that “We have come back from this postulate. Because if studies have shown a connection between blood group and severity of Covid cases, protection against infection has never been proven.

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