Maintaining immunological memory to the SARS-CoV-2 virus during COVID-19 pandemic

Abstract

The question of the duration and effectiveness of post-infection immunity to SARS-CoV-2 and its comparison with post-vaccination remains at the center of study by many researchers. The aim of the work was to study the duration of maintaining post-infection and post-vaccination immunity to the SARS-CoV-2 virus, as well as the formation of hybrid (vaccination after infection) and breakthrough (repeated disease or disease after vaccination) immunity in the context of an ongoing pandemic. 107 adults who had mild or moderate COVID-19 3-18 months after the disease and 30 people vaccinated twice with the Sputnik V vaccine were examined 1-6 times. Antibodies to the SARS-CoV-2 virus were determined by ELISA on the SARS-CoV-2-IgG quantitative-ELISA-BEST test systems. The avidity of antibodies was determined by additional incubation with and without denaturing solution. Mononuclear cells were isolated from blood by gradient centrifugation, incubated with and without coronavirus S-protein for 20 hours, stained with fluorescently labeled antibodies, and the percentage of CD8highCD107a+ was counted on a FACSCanto II cytometer. It was shown that in the group of reconvalescent and vaccinated, the level of antibodies specific to the virus decreased more pronounced in individuals with an initially high humoral response, but after 9 months the decrease slowed down and reached a plateau. The avidity of antibodies rose to 50% and persisted for 18 months. Cellular immunity in recovered patients did not change for 1.5 years, while in vaccinated patients it gradually decreased after 6 months, but remained at a detectable level. After revaccination of the vaccinated, a significant increase in the level of antibodies, avidity to 67.6% and cellular immunity to the initial level was noted. Hybrid immunity turned out to be significantly higher than post-infection and post-vaccination immunity. The level of antibodies increased to 1218.2 BAU/ml, avidity to 69.85%, and cellular immunity to 9.94%. Breakthrough immunity was significantly higher than after the first disease. The level of antibodies rose to 1601 BAU/ml, avidity - up to 81.6%, cellular immunity - up to 13.71%. Using the example of dynamic observation of four COVID-19 reconvalescents, it has been shown that in the context of the ongoing pandemic and active mutation of the coronavirus, natural boosting occurs both asymptomatically and as a result of a mild re-infection, which prevents the disappearance of humoral and cellular immunity specific to SARS-CoV -2.