On day 0, the COVID-19 patients had detectable seropositivity for the IgG1, IgG2, IgG3, and IgG4 S RBD-specific antibodies, ranging from 30% to 66.7% against the Wuhan strain, 30% to 66.7% against the Alpha variant, and 36.7% to 73.3% against the Delta variant, but the positive rates of these antibodies against the Omicron variant ranged from only 0% to 10% (Fig. 5). Here, IGHG3 is linked to COVID-19.