Similarly, declines in anti-S IgM titers, along with rapid decay of NAbs, were reported in recovered COVID-19 patients.23 These observations suggest that at least part of the neutralizing activity is mediated by anti-S IgM and could possibly explain the apparent paradox between the stable IgG levels and declining neutralization capacity following SARS-CoV-2 infection and vaccination. This evidence concerns the gene CD40LG and COVID-19.