Monitoring saliva responses to SARS-CoV-2 and HCoV longitudinally in sub-cohort B (n = 76, pre-infection B1, seroconverted B2), we observed that high pre-existing mucosal HCoV antibody responses were associated with high mucosal SARS-CoV-2 antibody response upon infection (IgG regression coefficient = 0.60, 95% CI = [0.088, 1.11], P = 0.025; not significant for IgA and IgM with regression coefficients = 0.20, 95% CI = [−0.023, 0.42], P = 0.084 and 0.19, 95% CI = [−0.063, 0.45], P = 0.14, respectively; Fig. 3C). The gene discussed is CD40LG; the disease is infection.