COVID-19 Infection and Efficacy of Vaccination in Patients with Rheumatic Diseases During Omicron Outbreak in South Korea: A Prospective Cohort Study

Background: Epidemiological data on the impact of the Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on patients with autoimmune inflammatory rheumatic diseases (AIRDs) is lacking. We investigated the incidence of coronavirus disease (COVID-19) caused by the omicron variant and its impact on patients with AIRDs.Methods: This prospective longitudinal study was performed between January and October, 2022 in South Korea. Patients were classified into AIRD and non-AIRD groups according to their underlying diseases. COVID-19 status, date of confirmed infection, and vaccination status were captured from the patient survey and national database. The COVID-19 incidence during the study period was examined and compared between the two groups. The effect of clinical factors on the infection rate was analyzed in the AIRD group.Findings: A total of 1814 patients (1535 and 279 in the AIRD and non-AIRD groups, respectively) were analyzed. During the study period, 857 COVID-19 cases were reported in 834 patients (46.0%). The infection rates in the AIRD and non-AIRD groups were comparable. In the AIRD group, older age (≥70 years) and glucocorticoid use were significantly associated with a lower rate of COVID-19 infection. The third booster vaccination significantly lowered the incidence of COVID-19 (adjusted hazard ratio, 0.85[0.73‒0.99]), and the prophylactic effect was more evident in patients aged <70 years (0.81 [0.69‒0.95], P value for interaction 0.046).Interpretation: The risk of SARS-CoV-2 infection with the Omicron variant did not increase in patients with AIRDs. The third booster vaccination regimen decreased the infection rate in patients aged <70 years.Funding: This research work was supported by Seoul National University Hospital Research Fund (Grant number: 0420220760).Declaration of Interest: All the authors have declared no financial, professional, or personal competing interests that might have influenced the performance or presentation of the work described in this manuscript.Ethical Approval: This study was conducted in accordance with tenets of the Declaration of Helsinki and approved by the Institutional Review Board of Seoul National University Hospital (IRB No. 2207-027-1337). Written informed consent was obtained from all patients.