CD40LG and viral infectious disease: Previous studies reported that the acute antibody responses to SARS-CoV-2 infection were similar to those in other viral infections, in which seroconversion takes place within 2 weeks and the IgG level peaks around 2 to 3 weeks after symptom onset.2, , –5,20 However, the kinetics of the IgM and IgG antibodies after reaching their maximum levels were yet to be clarified.