Long-term monitoring of the development and extinction of IgA and IgG responses to SARS-CoV-2 infection.

Despite the great interest of the scientific community in the behavior of the human body after contact with the new coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), long-term (more than 6 months) monitoring of the immunological status of patients with coronavirus disease 2019 (COVID-19) having varying severity degrees and of the people with a low SARS-CoV-2 viral load is practically absent. The aim of this study is a 9-month monitoring of SARS-CoV-2 infection immune response development and extinction using quantitative assessment of IgA and IgG levels in the blood of healthy donors living in the context of the coronavirus pandemic and of the patients who have undergone COVID-19. The project involved 180 volunteers, of whom 51 persons (28.33%) fell ill with COVID-19 during the observation period. All people who underwent COVID-19 developed a stable humoral immune response but their individual immune status had a number of features. Approximately 39.22% (20 of 51 people) of project participants diagnosed with COVID-19 showed an unusual change in plasma anti-SARS-CoV-2 IgA levels. Relatively high levels of IgA (ratio ~ 3) after recovery persisted for a long time (more than 6 months). In one-third (17 of 51 people) of patients with COVID-19, the IgA level exceeded the IgG level. IgA antibodies appeared earlier and showed a stronger and more robust response to the SARS-CoV-2 virus than IgG. Increased levels of anti-SARS-CoV-2 IgA (ratio from 0.8 to 2.36) throughout the observation period were recorded in 28 of 180 project participants (15.56%) of whom only one person fell ill with COVID-19.