Figure 1.

(A) SARS-CoV-2 structural antigens, used for immunoassays. Nucleocapsid and Spike proteins are the most abundant antigens, therefore, they are used for improved sensitivity. Antigen-subunits, as S1 and S2, or RBD and NTD, can provide more specific results. (B) The expected IgM/IgG curves following exposure to antigen through natural infection or vaccination. The maturation of immune response usually leads to initial IgM induction and, while titers of this antibody class decrease, IgG titers increase and persist for longer periods, which varies according to the pathogen considered. Below it, kinetics of SARS-CoV-2 antigens and antibodies detection is represented. Differently from the expected, titers of IgA, IgM, and IgG antibodies increase in parallel. The time to achieve seronegativity and the particularities of vaccine-induced humoral response are still being elucidated (figure created with BioRender).