Objectives To investigate temporal trends in incidence and severity of COVID-19 among patients with systemic autoimmune rheumatic diseases (SARDs) from the first wave through the initial Omicron wave.

Methods We conducted a retrospective cohort study investigating COVID-19 outcomes among patientswith SARD systematically identified to have confirmed COVID-19 from 1 March 2020 to 31 January 2022 at Mass General Brigham. We tabulated COVID-19 counts of total and severe cases (hospitalisations or deaths) and compared the proportion with severe COVID-19 by calendar period and by vaccination status. We used logistic regression to estimate the ORs for severe COVID-19 for each period compared with the early COVID-19 period (reference group).

Results We identified 1449 patients with SARD with COVID-19 (mean age 58.4 years, 75.2% female, 33.9% rheumatoid arthritis). There were 399 (28%) cases of severe COVID-19. The proportion of severe COVID-19 outcomes declined over calendar time (p for trend <0.001); 46% of cases were severe in the early COVID-19 period (1 March 2020–30 June 2020) vs 15% in the initial Omicron wave (17 December 2021–31 January 2022; adjusted OR 0.29, 95% CI 0.19 to 0.43). A higher proportion of those unvaccinated were severe compared with not severe cases (78% vs 60%).

Conclusions The proportion of patients with SARD with severe COVID-19 has diminished since early in the pandemic, particularly during the most recent time periods, including the initial Omicron wave. Advances in prevention, diagnosis and treatment of COVID-19 may have improved outcomes among patients with SARD.