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 Omicron wave. Methods: We conducted a retrospective cohort study investigating COVID-19 outcomes among SARD patients systematically identified to have confirmed COVID-19 from March 1, 2020 to January 31, 2022 at a large healthcare system in Massachusetts. We tabulated COVID-19 counts of total and severe cases (hospitalizations 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 to the early COVID-19 period (reference group). Results: We identified 1449 SARD patients with COVID-19 (mean age 58.4 years, 75.2% female, 33.9% rheumatoid arthritis). There were 399 (27.5%) cases of severe COVID-19. The proportion of severe COVID-19 outcomes declined over calendar time (p for trend <0.001); 45.6% of cases were severe in the early COVID-19 period (March 1-June 30, 2020) vs. 14.7% in the Omicron wave (December 17, 2021-January 31, 2022; adjusted odds ratio 0.29, 95%CI 0.19-0.43). A higher proportion of those unvaccinated were severe compared to not severe cases (78.4% vs. 59.5%). Conclusions: The proportion of SARD patients with severe COVID-19 has diminished since early in the pandemic, particularly during the most recent time periods, including the Omicron wave. Advances in prevention, diagnosis, and treatment of COVID-19 may have improved outcomes among SARD patients. KEY MESSAGES: What is already known about this subject?: Patients with systemic autoimmune rheumatic diseases (SARDs) may be at increased risk for severe COVID-19, defined as hospitalization or death.Previous studies of SARD patients suggested improving COVID-19 outcomes over calendar time, but most were performed prior to the wide availability of COVID-19 vaccines or the Omicron wave that was characterized by high infectivity.What does this study add?: The proportion of SARD patients with severe COVID-19 outcomes was lower over calendar timeThe adjusted odds ratio of severe COVID-19 in the Omicron wave was 0.29 (95%CI 0.19-0.43) compared to early COVID-19 period.The absolute number of severe COVID-19 cases during the peak of the Omicron variant wave was similar to the peaks of other waves.SARD patients with severe vs. not severe COVID-19 were more likely to be unvaccinated.How might this impact on clinical practice or future developments?: These findings suggest that advances in COVID-19 prevention, diagnosis, and treatment have contributed to improved outcomes among SARD patients over calendar time.Future studies should extend findings into future viral variants and consider the roles of waning immunity after vaccination or natural infection among SARD patients who may still be vulnerable to severe COVID-19.