23-29 november 2020
Do we have permanent immunity following infection ?
COVID-19, brought about by the SARS-CoV-2 virus, produces very different levels of severity. It’s necessary to understand the types of immunity that this infection can engender, from asymptomatic cases to fatal infection. And how much time immunity can last, since antibody production during the initial infection generally has a determining effect on the probability of falling ill, especially where there is re-infection.
Just as with diptheria or measles, it is possible, after a first infection or vaccination, to maintain production of IgGs (the majority antibody in our system) for decades. Likewise, in more than 90 COVID-19 patients at the convalescent phase it was possible to detect IgGs showing an affinity for the surface proteins N and S (Spike), in particular on the site of the Spike protein that allows the virus to fix itself to the cell, known as an RBD. These specific qualities make them good neutralizing antibodies since they are capable of specifically recognizing the virus and preventing infection. Generally it has been possible to correlate the production of IgGs with the age of the patient, as well as the severity of the SARS-CoV-2 infection. So the more severe the symptoms of COVID-19, the more the body will produce igGs, anti-S, anti-N and anti-RBD antibodies.
Over time, this production decreases. However, the study of the production of antibodies in moderately affected patients has shown that in certain individuals, good levels of IgGs were present over a 3 month period. These patients had symptoms over a shorter period despite an initial distribution of anti-SARS-CoV-2 IgGs that was similar to other patients.
In order to explain this discrepancy, a study of the T-cells of these same patients was carried out. Results showed that patients with a longer term production of IgGs also had more CD4 memory T-cells, necessary for the maturing of plasma cells and antibody production.
These differences may be the result of intrinsic factors in patients or, perhaps, stem from a prior immunization by viruses of the same family. This prior immunization may generate an optimized anti-SARS-CoV-2 response due to the presence of memory B lymphocytes having already recognized other coronaviruses.