Salivary antibodies mirror systemic humoral immunity to SARS CoV-2 and reveal sex-specific differences in salivary anti-spike IgA and IgG levels

Durable antibody responses are essential for long-term protection against SARS-CoV-2. We assessed the utility of point-of-care lateral flow tests (LFTs) versus ELISA in monitoring systemic and mucosal immunity and explored saliva as a surrogate for serum antibody measurement. 450 participants were recruited in a university and serum and saliva samples were analysed for anti-Spike IgA and IgG antibodies using ELISA, and for nucleocapsid (N) and neutralising Spike antibodies via LFT. Despite only 46% self-reporting prior infection, 95% had detectable N antibodies. Serum demonstrated higher anti-Spike IgA and IgG positivity than saliva. Moderate correlations between serum and salivary IgA and IgG were observed. LFT band intensity significantly correlated with ELISA-derived antibody levels. Sex-specific differences in salivary anti-Spike IgA and IgG levels were identified, with males displaying higher levels in early post-exposure periods. These findings support LFTs and saliva sampling as accessible tools for monitoring SARS-CoV-2 immunity and guiding booster vaccination strategies.