The comprehension of a long-term humoral immune response against SARS-CoV-2 can shed light on the treatment and vaccination strategies of COVID-19 disease, improving the knowledge about this virus infection and/or re-infection. We assessed the IgG antibodies against SARS-CoV-2 nucleocapsid (N) protein (anti-SARS-CoV-2 (N) IgG) in 1441 COVID-19 convalescent patients within 15 months longitudinal study from middle-developed country. The main inclusion criteria was positive RT- PCR result on nasopharyngeal swab samples at least one month before antibody testing and absence of any induced or inherited immunodeficiency. 92.7% of convalescent patients' serum contained anti-SARS-CoV-2 (N) IgG and only 1.3% of patients had a delayed antibody response. In the majority of convalescent patients' the durability of antibodies lasted more than one year. The kinetics of anti-SARS-CoV-2 (N) IgG took a bell-shaped character-increased first 25-30 weeks, then started to decrease, but were still detectable for more than 15 months. We found that on the one hand anti-SARS-CoV-2 humoral response level correlates with disease severity, on the other, in particular, the level of peak antibodies correlates with age-older patients develop more robust humoral response regardless of sex, disease severity and BMI.
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