pone.0344308.t005 -

BackgroundUnderstanding post-infection immunity with the first SARS-CoV-2 variant may provide valuable insights into the duration and effectiveness of the humoral immune response. This study aims to characterize the serological profile of naïve individuals infected with the first SARS-CoV-2 variant.MethodsA prospective study with repeated measures was conducted in Tunisia, from March to October 2020, during the first wave of COVID-19. Adults confirmed with confirmed COVID-19 were monitored during the first wave of the pandemic. ELISA blood tests were conducted at multiple intervals: day 7, day 14, and at 1, 2, 3, 4, and 6 months post-infection.Results173 serum samples were collected from immunologically naïve individuals infected with the first circulating SARS-CoV-2 variant, ranging from 7 days to 6 months post-RT-PCR confirmation. The study revealed a robust humoral immune response in most participants, with 94.1% testing positive for IgM anti-N, 88.2% for IgM anti-S, 98% for IgG anti-N, and 100% for IgG anti-S antibodies. Anti-N IgM antibodies peaked at days 14 and 30 with high positive values (>0.260), while anti-S IgM antibodies showed elevated levels (>0.990) at days 7 and 14. For IgG, anti-N antibodies reached their highest levels (>0.810) at month 4, while anti-S IgG antibodies maintained high positive values (>0.490) at days 7 and 14, and remained elevated at months 4 and 6. No significant differences in antibody levels were observed based on gender, age, comorbidities, or symptoms presence.ConclusionA typical adaptive immune response was observed in naïve individuals infected with the initial SARS-CoV-2 variant, showing typical IgM and IgG antibody production from day 7 to month 6. We specifically investigated immunologically naïve individuals infected with the first circulating SARS-CoV-2 variant, from the earliest stage of infection, a context that is no longer reproducible.