Low and transient salivary neutralizing antibodies after COVID vaccination

Abstract Neutralizing activity found in the blood following intramuscular vaccination protects against systemic disease from SARS-CoV-2 infection. Mild breakthrough mucosal infections in vaccinated individuals can contribute to transmission chains of infection, and as such the contribution of intramuscular vaccination to mucosal immunity is important to understand. We assessed vesicular stomatitis virus (VSV) SARS-CoV-2 SPIKE protein neutralization activities as well as anti-viral spike and RBD IgG and IgA isotype antibody binding, in saliva from individuals who had recovered from SARS-CoV-2 infection and people who received immunization. The various vaccination strategies deployed globally showed key differences in the extent of neutralizing activity that could be measured. Even in subjects with significant peak activity 2–4 weeks following a second dose of mRNA vaccination, this neutralizing activity was transient and significantly reduced within 3–6 months. Among adenoviral vectors, ChAdOx1 elicited significantly more salivary neutralizing activity and antibody levels compared to Ad26.S. A large range of salivary neutralizing activity is induced following different intramuscular SARS-COV-2 vaccination strategies. All were orders of magnitude lower than neutralization levels observed in blood, and it remains to be determined if any of the observed neutralizing activity in the saliva can neutralize virus in the upper respiratory tract upon exposure. Based on studies where high levels of mucosal IgA antibodies were induced in response to stimulation with aerosol intranasal vaccines, such vaccines could be important in lowering transmission of SARS-COV-2. Supported by The Fairbairn Foundation and SPARK