Covid-19: why some people have never been infected by the disease ?

Covid-19 : pourquoi certains individus n’ont-ils jamais été infectés ?

People who have never been infected with the SARS-CoV-virus have a previously unknown immune response that would protect them, according to a study whose results have just been published in the journal Nature. Explanations.

They are called the Novid. These are the individuals who, since the beginning of the appearance of SARS-CoV-2 and despite the successive waves of the epidemic, have never caught Covid-19. A study, published in the journal Nature, seems to have uncovered their secret.

Researchers have just discovered that people who consistently manage to avoid illness have unique immune responses that help them avoid prolonged infection. The results of the study suggest "an immune response localized in the mucous membrane of the nose and which allows individuals to identify the virus, to prevent it from spreading ;rsquo;anchor and cause infection", details l’Imperial College London, establishment which co- directed this work, in a press release.

The path of the infection under the microscope

To reach these conclusions, the scientists conducted a human challenge study – candidates volunteered to be infected with the virus. 36 adults, in good health, with no history of Covid-19 infection or vaccination against Covid-19, were administered the virus through the nose.

The team of researchers carried out detailed monitoring of the blood and mucous membrane of the nose before, during and after infection. It is the entire path of the infection until its total disappearance which has been scrutinized. In total, the sequencing of more than 600,000 cells was carried out!

In each participant, the team discovered immune responses that were specific to them. In individuals who immediately cleared the virus, researchers did not observe a generalized immune response as we know it, but developed immune responses "never seen previously", notes the press release of Imperial College. The cells involved in this hitherto unknown immune response could also be identified.

In addition to this discovery, the study establishes an extremely complete chronology of the responses of the immune system during an infection. Scientists have thus discovered the involvement of a gene in the prevention of prolonged infection.

The starting point for new treatments ?

For Prof. Chirstopher Chiu, of the Department of Infectious Diseases of the Imperial College London, "Not only will these findings have an important impact on the development of next-generation interventions against SARS-CoV-2, but they are also expected to be generalizable to other future epidemics and pandemics" .

As for Dr. Marko Likolic, of University College London: "These results shed new light on the crucial early events that allow the virus to settle or eliminate it quickly before symptoms develop. We now have a much better understanding of all immune responses, which could serve as a basis for developing potential treatments and vaccines.