Abstract
OBJECTIVE: To assess factors associated with serologic response to the coronavirus 2019 (COVID-19) booster vaccine in patients with autoimmune rheumatic diseases treated with rituximab (RTX) who were previously serologically unresponsive to the initial vaccine series. METHODS: A retrospective chart review of patients treated with RTX who failed to demonstrate a serologic response to the first SARS-CoV-2 vaccination series and subsequently received an mRNA vaccine booster was performed. Serologic response ≥ 4 weeks after the booster was the primary outcome. Fisher exact tests, t tests, and Wilcoxon rank-sum tests were used for comparisons. RESULTS: In 31 patients who were previously seronegative, 68% seroconverted following a booster of the COVID-19 vaccine. B cell reconstitution was significantly different between those with positive (median 1.79, IQR 0.65-3.00) and negative (median 0, IQR 0-0) serologic responses to the booster. The days from last RTX dose were also statistically different among seroconverters (median 301, IQR 251-368) vs nonseroconverters (median 188, IQR 169-245). Demographic characteristics were not associated with serologic positivity. Positive predictive value of B cell presence was 90.9% (95% CI 70.8-98.9) and negative predictive value was 100% (95% CI 59-100) for serologic response to the mRNA booster vaccine. Positive predictive value of time ≥ 6 months from last RTX dose to booster was 78.3% (95% CI 56.3-92.5) and the negative predictive value was 62.5% (95% CI 24.5-91.5). CONCLUSION: Detectable B cells and longer time from last RTX exposure were associated with the development of anti-SARS-CoV-2 spike protein antibodies following the booster vaccine. These findings should be considered in timing boosters in patients treated with RTX.