In the early phase of the disease, within one week of the symptom onset, the titers of all the antibody types described above, except IgM(N), were higher in COVID-19 patients belonging to severity group 2b or 3, which suggested the possible usefulness of antibody testing to identify the subgroup of patients who would require oxygen supplementation at high flow rates. The gene discussed is CD40LG; the disease is COVID-19.