Detection of anti-SARS-CoV-2 antibodies in tears: Ocular surface immunity to COVID-19

PURPOSE: To evaluate the presence of SARS-COV-2 specific IgA and IgG antibodies in tears of unvaccinated and anti-COVID-19 vaccinated subjects with previous history of SARS-COV-2 infection. To compare results in tears with those in saliva and serum and correlate with clinical data and vaccination regimens. METHODS: Cross-sectional study including subjects with a previous history of SARS-CoV-2 infection, both unvaccinated and vaccinated against COVID-19. Three samples were collected: tears, saliva and serum. IgA and IgG antibodies against S-1 protein of SARS-CoV-2 were analyzed with a semi-quantitative ELISA. RESULTS: 30 subjects, mean age 36.4 ± 10, males 13/30 (43.3%) with history of mild SARS-CoV-2 infection were included. 13/30 (43.3%) subjects had received a 2-dose regimen and 13/30 (43.3%) a 3-dose regimen of anti-COVID-19 vaccine, 4/30 (13.3%) subjects were unvaccinated. All the participants with full anti-COVID-19 vaccination (2-or 3-doses) presented detectable anti-S1 specific IgA in all three biofluids, tears, saliva and serum. Among unvaccinated subjects, specific IgA was detected in 3/4 subjects in tears and saliva, whereas IgG was not detected. Considering IgA and IgG antibodies titers, no differences were observed between the 2- and 3-dose vaccination regimen. CONCLUSIONS: SARS-CoV-2-specific IgA and IgG antibodies were detected in tears after mild COVID-19, highlighting the role of the ocular surface as a first line of defense against infection. Most naturally infected unvaccinated individuals exhibit long-term specific IgA in tears and saliva. Hybrid immunization (natural infection plus vaccination) appears to enhance mucosal and systemic IgG responses. However, no differences were observed between the 2- and 3-dose vaccination schedule.