Association of Vaccination with <scp>COVID</scp> Outcomes in Pregnant People with Autoimmune Diseases: A Retrospective National Cohort Analysis

OBJECTIVE: To evaluate the effectiveness of COVID-19 vaccination in reducing incident and severe COVID-19 among pregnant individuals with autoimmune rheumatic diseases (AIRDs). METHODS: We conducted a retrospective cohort study using national electronic health records, including 270,811 pregnant individuals aged 15-55 with pregnancies between December 10, 2020, and June 1, 2024. Among them, 4,715 (1.5%) had at least one AIRD (rheumatoid arthritis, spondyloarthritis, or systemic lupus erythematosus). Participants were categorized by AIRD and vaccination status (unvaccinated, initially vaccinated, or booster vaccinated). Time to incident and severe COVID-19 was assessed using adjusted time ratios (TRs), stratified by variant period (pre-Omicron vs. Omicron). RESULTS: Initial vaccination delayed time to COVID-19 during the pre-Omicron period in individuals with AIRDs (TR: 1.095; 95% CI: 1.036-1.157), but not during Omicron (TR: 1.039; 95% CI: 0.980-1.102). Booster vaccination was not significantly protective against infection (TR: 1.039; 95% CI: 0.958-1.128) or severe outcomes (TR: 1.119; 95% CI: 0.670-1.867). Compared to vaccinated individuals without AIRDs, those with AIRDs had shorter time to breakthrough infections in both pre-Omicron (TR: 0.940; 95% CI: 0.891-0.991) and Omicron (TR: 0.905; 95% CI: 0.858-0.955) periods, and to severe disease during Omicron (TR: 0.631; 95% CI: 0.485-0.821). CONCLUSION: Vaccination is associated with protection against COVID-19 in pregnancy, but its effectiveness is reduced in those with AIRDs, particularly during the Omicron period.