Coronavirus: immunity could last months, but even years

This is the hypothesis of a team of researchers who, analyzing the blood samples of patients recovered from the coronavirus, observed how the immune response is powerful and could last a long time, even for several years

(photo : Getty Images) Once recovered from the coronavirus, how long is there no risk of re-infection? This is one of the crucial questions that the scientific community has been trying to answer since the start of the Covid-19 pandemic. And today, to add to the growing body of research that is trying to shed light on immunity, comes a new study according to which most people have enough immune cells to prevent disease even after months, even years. We specify immediately that although the study has not yet been reviewed and published, therefore, in a scientific journal, as reported by the New York Times, it is the most detailed on the coronavirus immune memory carried out so far. And in any case it is available in pre-print on biorxiv.

To understand that coronavirus immunity may be long-term, researchers recruited 185 participants, aged 19 to 81, who had recovered from Covid-19, and who had developed mild symptoms that did not required hospitalization. From their blood samples taken in the months after healing, the team tracked four components of the immune system over time: antibodies, B cells (which produce more antibodies as needed), and two types of T cells (or T lymphocytes). that specifically fight the virus. From the analyzes, the researchers observed that antibodies and T cells showed a modest decline six to eight months after infection, memory B cells even grew in number six months after healing, the latter. totally unexpected and still not fully understood. A slow decline in the short term, the researchers explain, would suggest that immune cells can remain in the body for a very long time. "This amount of immune memory would likely prevent the vast majority of people from contracting a hospital-requiring, and therefore more serious, disease for many years," commented study author Shane Crotty, virologist at La Jolla Institute of Immunology.

The exact duration of immunity is difficult to predict because the scientific community does not yet know what levels of the different immune cells are needed to provide protection from the coronavirus. However, the results of this study are consistent with those released by other laboratories. For example, researchers from the University of Washington had already shown that some memory cells produced as a result of infection persist for at least three months in the body. While another preliminary study, published last week on bioRxiv, showed that T-cell-mediated immunity could last up to six months, even in asymptomatic patients and in those who have developed mild forms of the disease. "These studies all show broadly the same picture, which is that once those critical first weeks have passed, the rest of the immune response appears to be quite predictable," Deepta Bhattacharya, an immunologist at the University of Arizona, told the journal. br>
We also remember that these results represent a sort of relief for the scientific community, given the reports in recent months that the rapid decline in antibody levels would mean that the immune defense against the coronavirus could disappear in a few months. But, as many immunologists recall, in addition to the fact that it is natural that they decrease in a short time, antibodies represent only part of the protection put in place by the immune system. Although antibodies in the blood are needed to block the virus and prevent a second infection, the immune cells that "remember" the virus are responsible for preventing serious illness. “What we need to understand is whether or not reinfection will be a problem. And so having the evidence to suggest a persistent and robust type of response, at least at these time scales, is very encouraging, "explained Jeffrey Shaman, of Columbia University, they point out that at least to date coronavirus re-infections seem to be quite rare.