However, with the transient nature of salivary IgM responses and the low sensitivity of salivary assays for anti-SARS-CoV-2 S1 or S1 RBD IgM [26], the negative results observed here for SARS-CoV-2 S1 RBD-binding IgM in all tested samples cannot be conclusively interpreted as evidence of an absence of infection history. This evidence concerns the gene CD40LG and infection.