The question of the immunity of people cured of Covid-19 is still subject to debate within the scientific community. A recent pre-publication study estimates that some of these patients never developed antibodies!
Many of the patients with Covid-19 had only mild symptoms and recovered easily. And yet, some of these individuals would never have developed antibodies . This conclusion is that of a British study pre-published on the medRxiv platform on June 9, 2020. As part of this study, the researchers analyzed the level of type G antibodies or immunoglobulins (IgG) in 177 patients, and this over a period of two months. In addition, they were declared positive for Covid-19 by means of a PCR test. According to the results, between 2 and 8.5% of patients have not developed any antibodies!
The study indicates that the production of antibodies is proportional to the intensity of the symptoms. In other words, patients who have developed a severe infection are more likely to have developed antibodies. This would also be the case for the elderly, obese and with hypertension. At the bottom of the scale, we find asymptomatic people. For the researchers, the immune response could therefore be linked to the inflammatory response . It could also be that a higher viral load stimulates inflammation and antibody production more.
On the other hand, the absence of antibodies does not necessarily mean an absence of immunity. Researchers refer to “immune responses limited to other antigens or mediated by T cells” . It must be said that another study (this time German) had in April 2020 mentioned a possible cross-immunity between the common cold and Sars-CoV-2 (Covid-19). It could also be that the mild infections involved only the cells of the mucous membranes of the respiratory tract. In this specific case, the antibodies would remain undetectable in the immune system overall but should be present in the stool.
The debate continues to rage since the British study contradicts a French study from May 2020, conducted jointly by the Institut Pasteur and the Strasbourg University Hospital. This research indicated that 98% of patients with by Covid-19 had developed neutralizing antibodies. Incidentally, let us emphasize the fact that the three studies referred to in this article were all published on the pre-publication platform medRxiv. Thus, the latter must be validated by peers.
Let's also mention the fact that no one really knows what level of antibodies is ideal for good immunity and how long these same antibodies remain in the body. Anyway, this lack of consensus on this subject could make it even more difficult to develop a vaccine . Indeed, a vaccine confers sterilizing immunity but does not necessarily prevent an infection of the respiratory tract. In this case, the vaccine could onlymake the symptoms less severe.
