Vaccination induced antibody and T-cell immune responses are important for systemic protection from COVID-19. Because SARS-CoV-2 infects and is transmitted by oral-pharyngeal mucosa, we wished to test mucosal antibodies elicited by natural infection or intramuscular vaccine injection. In a non-randomized observational study, we measured antibodies against the SARS-CoV-2 RBD in plasma and saliva from convalescent or vaccinated individuals and tested their neutralizing potential using a replication competent rVSV-eGFP-SARS-CoV-2. We found IgG and IgA anti-RBD antibodies as well as neutralizing activity in convalescent plasma and saliva. Two doses of mRNA vaccination (BNT162b2 or mRNA-1273) induced high levels of IgG anti-RBD in saliva, a subset of whom also had IgA, and significant neutralizing activity. We detected anti-RBD IgG and IgA with significant neutralizing potential in the plasma of single dose Ad26.COV2.S vaccinated individuals, and we detected slight amounts of anti-RBD antibodies in matched saliva. The role of salivary antibodies in protection against SARS-CoV-2 infection is unknown and merits further investigation. This study was not designed to, nor did it study the full kinetics of the antibody response or protection from infection, nor did it address variants of SARS-CoV-2.
Although SARS-CoV-2 infects the upper respiratory tract, we know little about the amount, type, and kinetics of antibodies (Ab) generated at this site in response to intramuscular COVID-19 vaccination, and whether these Ab protect against subsequent "breakthrough" infections. We collected longitudinal serum and saliva samples from participants receiving two doses of mRNA COVID-19 vaccines over a 6-month period and measured the relative level of anti-Spike and anti-Receptor Binding Domain (RBD) Ab. We detected anti-Spike/RBD IgG and IgA and associated secretory component in the saliva of most participants receiving 1 dose of mRNA vaccine. Administration of a second dose of mRNA boosted the IgG but not the IgA response, with only 30% of participants remaining positive for IgA at this timepoint. At 6 months post-dose 2, these participants exhibited greatly diminished anti-Spike/RBD IgG and IgA levels concomitant with a reduction in neutralizing activity in the saliva, although the level of secretory component associated anti-Spike was less susceptible to decay. Examining two prospective cohorts of subjects that were monitored for infections post-vaccination, we found that participants who were subsequently infected with SARS-CoV-2 had lower levels of vaccine-induced serum anti-Spike/RBD IgA at 2-4 weeks post-dose 2 compared to participants who did not experience an infection, whereas IgG levels were comparable between groups. These data emphasize the importance of developing COVID-19 vaccines that elicit a durable IgA response. One-Sentence SummaryOur study delves into whether intra-muscular mRNA vaccination regimes confer a local IgA response in the oral cavity and whether the IgA response is associated with protection against breakthrough infection.
