Effectiveness of delayed second dose of AZD1222 vaccine in patients with autoimmune rheumatic disease.

There is paucity of data on extended dosing interval between two doses of AZD1222 (AstraZeneca) in patients with Autoimmune Rheumatic Diseases (AIRD). We aimed to study the humoral response and rate of breakthrough infections between the two groups who had received the second dose of vaccine at 4 weeks (Group 1) and 10-14 weeks (Group 2). From established cohort [COVID-19 vaccination cohort from CARE(CVCC)] of vaccinated patients with AIRD, those who had received AZD1222 were included and divided into two groups. Anti-Receptor Binding Domain (RBD) antibodies (IU/ml) were measured 1 month after the second dose. Its predictors and rate of breakthrough infections were studied. Four hundred ninety-five patients with AIRD were included in this study. Group 2 had higher anti-RBD antibody titres [1310.6 (±977.8) and [736 (±864.7), p = 0.0001. On univariate analysis, presence of Diabetes Mellitus; use of Methotrexate, Sulfasalazine, and Mycophenolate Mofetil; and vaccine interval were significantly associated with anti-RBD antibodies. Diabetes Mellitus and vaccine interval were independent predictors on multivariate analysis. Breakthrough infections were higher in Group 1 numerically on survival analysis but the difference was not significant (7.5% and 4.5%; log rank test: p = 0.25). In conclusion, increasing the gap between doses of the AZD1222 vaccine from 4 week to 10-14 weeks was found to be more beneficial in terms of antibody response in patients with AIRD. There was a trend towards higher breakthrough infections in the short interval group, supporting the antibody data. Key Points • There is paucity of data on effectiveness of increased dosing interval from 4-6 to 10-14 weeks for AZD1222 in patients with AIRDs • We observed a better humoral response with increased dosing interval with the interval and Diabetes Mellitus being independent predictors of the anti-RBD antibody levels • Breakthrough infections were numerically higher in the short interval group but the difference wasn't significant.