While immunoglobulin A (IgA) and immunoglobulin M (IgM) antibody levels in saliva decay shortly after infection, IgG antibodies against SARS-CoV-2 proteins persist and remain detectable for up to 9 months, demonstrating that salivary IgG is a reliable target for detecting antigen-specific antiviral antibody responses [26, 27, 30]. This evidence concerns the gene CD40LG and infection.