Antibody dynamics and viral load in COVID-19: differences in mild, moderate and severe cases

In this study, we investigated the potential association between the severity of COVID-19 (coronavirus disease 2019) and nasopharyngeal viral loads or serum antibody levels and evaluate the temporal dynamics of antibodies against SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). Using ELISA (enzyme-linked immunosorbent assay), we determined the presence of IgA, IgM and IgG antibodies in 450 serum samples from 122 patients for a period of 9 months after disease onset. Viral burden was quantified by RT-PCR (reverse transcription polymerase chain reaction) in 270 nasopharyngeal swab samples from 122 patients for a period of 4 weeks after the onset of the symptoms. Higher antibody values were generally seen in patients with moderate and severe disease compared to patients with mild COVID-19. Significant differences were established in IgA and IgG antibody levels at weeks 3-4 and 5-13 after the disease onset. In all severity groups, seroconversion rates were high and a similar pattern was observed with IgM antibodies quickly decreasing after reaching peak levels and IgA and IgG antibodies persisting at high values up to 9 months. The mean viral loads were higher in the mild group during the first 2 weeks and in the moderate and severe groups later on. However, the differences were not statistically significant. The IgA and IgG antibody response was significantly stronger in patients with moderate/severe disease around the time of peak antibody production as well as in vaccinated patients. No definitive association between viral load levels and the severity of COVID-19 was observed.