CD40LG and COVID-19: Some limitations still remain in this study: For one, although the transmission route of all cases was relatively clear and complete, data only came from local patients of Putian, so no multi-center data were accessed; for another, although COVID-19 antibodies IgM and IgG were detected, RBD antibody was not measured and immunofunctional assessments of the effect of T cell-mediated response on the delayed IgG antibody response in children were not conducted.