Most persons infected with SARS-CoV-2 display an antibody response between day 10 and day 21 after infection. Detection in mild cases can take longer time (four weeks or more) and in a small number of cases antibodies (i.e., IgM, IgG) are not detected at all (at least during the studies’ time scale). Based on the currently available data, the IgM and IgG antibodies to SARS-CoV-2 develop between 6–15 days post disease onset . The median seroconversion time for total antibodies, IgM and then IgG were day-11, day-12 and day-14 post symptom onset, respectively. The presence of antibodies was detected in <40% among patients within 1 week from onset, and rapidly increased to 100% (total antibodies), 94.3% (IgM) and 79.8% (IgG) from day-15 after onset.
The longevity of the antibody response is still unknown, but it is known that antibodies to other coronaviruses wane over time (range: 12 – 52 weeks from the onset of symptoms) and homologous re-infections have been shown. SARS-CoV-2 IgM and IgG antibody levels may remain over the course of seven weeks or at least in 80% of the cases until day 49. In comparison, one in ten of SARS-CoV-1 infected patients have been shown to maintain IgG antibodies for two years. In addition, it could be important to detect nasal IgA antibodies, as the serum IgA antibodies were not raised, but IgA persisted in the nasal mucosa one year post-infection for seasonal coronavirus.
Longitudinal serological studies that follow patients’ immunity over an extended period of time would be required to study the duration of immunity .
Reinfections with all seasonal coronaviruses occur in nature, usually within three years.
