RESUMEN
The determination of durability and vaccine-associated protection is essential for booster doses strategies, however data on the stability of SARS-CoV-2 immunity are scarce. Here we assess anti-SARS-CoV-2 immunogenicity decay and incident cases six months after the 2nd dose of Sinovac-CoronaVac inactivated vaccine (D210) in 828 autoimmune rheumatic diseases patients compared with 207 age/sex-balanced control individuals. The primary outcome is the presence of anti-S1/S2 SARS-CoV-2 IgG at 6 months compared to 6 weeks after 2nd vaccine dose for decay evaluation. Secondary outcomes are presence of neutralizing antibodies, percent inhibition by neutralizing, geometric mean titers and cumulative incident cases at 6 months after 2nd dose. Anti-S1/S2 IgG positivity and titers reduce to 23.8% and 38% in patients (p < 0.001) during the six-month follow up and 20% and 51% in controls (p < 0.001), respectively. Neutralizing antibodies positivity and percent inhibition declines 41% and 54% in patients (p < 0.001) and 39.7% and 47% in controls (p < 0.001). Multivariate logistic regression analysis show males (OR = 0.56;95% CI0.40-0.79), prednisone (OR = 0.56; 95% CI0.41-0.76), anti-TNF (OR = 0.66;95% CI0.45-0.96), abatacept (OR = 0.29; 95% CI0.15-0.56) and rituximab (OR = 0.32;95% CI0.11-0.90) associate with a substantial reduction in IgG response at day 210 in patients. Although cellular immunity was not assessed, a decrease of COVID-19 cases (from 27.5 to 8.1/100 person-years; p < 0.001) is observed despite the concomitant emergence and spread of the Delta variant. Altogether we show a reduction in immunity 6-months of Sinovac-CoronaVac 2nd dose, particularly in males and those under immunosuppressives therapies, without a concomitant rise in COVID-19 cases. (CoronavRheum clinicaltrials.gov:NCT04754698).