Mucosal immunity and antibody anergy in COVID-exposed Covishield vaccinees

Knowledge is limited on mucosal immunity induction and longitudinal responses to vaccination against SARS-CoV2. Here, we determined serum/salivary antibodies and cytokines after three Covishield vaccine doses. Sera from 205 healthcare workers (HCWs) one-month after first- dose; one-, three- and six-months after second-dose; paired sera and stimulated whole mouth fluid (SWMF) from 10 HCWs one-, three- and six-months after third-dose were tested for anti- spike SARS-CoV2 antibodies by ECLIA and for cytokines by ELISA/cytokine bead arrays. One-month after second-dose, antibodies had increased significantly (6-fold) in COVID-naive group, but declined (1.5-fold) in those previously exposed to COVID. At one-month after first- dose, IL-10 levels were statistically higher in the previously COVID-exposed group compared to COVID-naive group (p<0.02). Breakthrough infections were 44% in COVID-naive group, while re-infections were 27% in COVID-exposed group (p<0.02). Proinflammatory cytokines-IL- 17/IL-21 at one-month after first- and second-doses, and memory cytokines-IL-7/IL-15 at three- and six-months after second-dose were minimal. Antibodies spiked at one-month after third- dose and declined by three- and six-months after third-dose similar to post-second-dose. Paired sera and SWMF at one- and six-months after third-dose lacked adaptive immunity cytokine expression. Innate immunity cytokines (MIG, MCP-1, IL-8, TNF-, IL-6, IL-1{beta}) showed a declining trend in serum, but were sustained in SWMF. Thus, our findings suggest that first-dose acts as an antibody boost, while second-dose induces antibody anergy in the previously COVID- exposed group. Rapidly declining antibodies and minimal T cell cytokines raises concerns over their durability in subsequent virus exposures. Sustained innate cytokines emanating from the oral mucosa warrant further in-depth explorations.