CD40LG and Immunodeficiency: Hence, for the patient shown in Fig. 3E, the immune system starts to take effect from the second timepoint, when SARS-CoV-2-specific IgG level also starts to increase; however, the other 2 cases (Fig. 3F, G) do not show convincing SARS-CoV-2-specific IgM signal, suggesting possible immune deficiency or insufficient immunization.