However, we did not measure IgG subclass levels (ie, IgG1 and IgG3), which have also been associated with COVID-19 severity as well as age effects.15,46 In our study, we observed a decrease in levels of IgG-positive memory B cells among seropositive adults that corresponded with an increase in transitional B-cell levels. This evidence concerns the gene IGHG3 and COVID-19.