CD40LG and COVID-19: Among the COVID-19 patients at day 0, the IgM, IgA, and IgG seropositivity was 36.7% to 63.3% for the Wuhan strain, 23.3% to 60.0% for the Alpha variant, 16.7% to 43.3% for the Delta variant, and 3.3% to 16.7% for the Omicron variant (Fig. 5).