Abstract
The immune system produces antibodies following SARS-CoV-2 infection and vaccination. However, we lack comprehensive information about the humoral responses after infection and vaccination, which are similar but might differ in type or amount of produced antibodies. Therefore, we compared different types and amounts of antibodies produced by the immune system in response to infection versus those produced by BNT162b2 (Pfizer/BioNTech) vaccines. Our findings indicated that naturally infected individuals had 14-fold higher anti-SARS-CoV-2 spike protein (anti-S) and 41-fold higher anti-SARS-CoV-2 receptor-binding domain of the viral spike protein (anti-RBD) IgM titers than SARS-CoV-2-naïve vaccinees. Remarkably, naturally infected individuals maintained high levels of IgM antibody titers up to six weeks after symptom onset. A significantly rapid increase in anti-S IgG titers in primary infection was observed, eventually reaching a level similar to that in people who had third booster vaccination. This study revealed the characteristics of the target antigen and immunoglobulin isotypes after natural SARS-CoV-2 infection and COVID-19 vaccination.
