SARS-CoV-2-specific IgM antibody level peaks at week 3 and then declines, whereas IgG antibodies to spike protein can persist long-term, even beyond 1 year after infection (Gudbjartsson et al., 2020; Hou et al., 2020, 2021; Xiao A.T. et al., 2020). Here, CD40LG is linked to infection.