Immunity to Covid-19 may last for at least a year, according to two recent studies cited in the New York Times. The studies looked at a group of patients who contracted the disease about a year ago, and analyzed the robustness of their potential immune response to the virus.
The results revealed that those who recovered and were subsequently vaccinated, would not need additional immunizations. On the other hand, those who had never contracted the disease, despite being vaccinated, would most likely need to take additional doses.
Key to this process are the memory cells, or B lymphocytes, which, in contact with the virus, store all the information in the bone marrow, thus remaining capable, at any time, of producing antibodies. These same cells will then have the ability to strengthen themselves for at least 12 months after infection. According to the NY Times, this evidence counters fears that, as with many colds caused by other types of coronavirus, immunity to SARS-CoV-2 might be short-lived.
The reason we get infected repeatedly by common coronavirus has more to do with variation in the viruses themselves and less to do with immunity
Scott Hensley, immunologist at the University of Pennsylvania
The ideal formula for lasting immunity, the studies conclude, is simple: those who recovered from the infection and then were vaccinated, have an enormous capacity to fight the virus and even its variants.
On the other hand, this kind of protection is unlikely to be achieved by vaccination alone, which means that those who have not contracted or will not contract the disease may need additional vaccinations beyond the first one. This is also a question that is still under study.
People who are infected and vaccinated have a fantastic response, a fantastic set of antibodies, because they continue to evolve antibodies. I predict that they will remain active for a long time
Michel Nussenzweig, immunologist
For a year, the blood of 77 recovered patients was analyzed to understand how their immune systems reacted. Four months after the infection, the level of antibodies dropped dramatically, a trend that was seen in the following months. This was a fact that was expected by the researchers and did not necessarily mean that the individuals had reduced protection. If the blood contained large amounts of antibodies to all the diseases our bodies fought, the blood would quickly turn into a thick liquid.
Although the antibodies decrease, the memory B-cells are kept ready in the bone marrow for when it is necessary to activate the creation of new antibodies again. However, this does not happen in all cases, which means that even those who have recovered should be vaccinated.
Another study that followed 63 recovered patients revealed that they kept their protection intact for six to 12 months after their first contact with Covid-19. Even in this period, there was a maturation and evolution of memory B cells, which became more effective at fighting the disease and its variants.
In the non-vaccinated patients, however, this protection was lower after one year. This result underlined the importance of vaccination, even in those who have already had contact with the disease. Natural immunity and vaccination would thus be the perfect combination.
