Changes in serious infection and mortality among patients with ANCA-associated vasculitis during the COVID-19 pandemic: an interrupted time-series analysis of J-CANVAS.

Objectives: In antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, infection risk exceeds that of the general population, and infection is a leading cause of death. However, the impact of the COVID-19 pandemic on serious infections and mortality in this population remains uncertain. Methods: This observational study used data from the nationwide registry in Japan (Japan Collaborative Registry of ANCA-Associated Vasculitis), which includes patients with newly diagnosed and relapsed ANCA-associated vasculitis from 29 sites between January 2017 and March 2023. The primary outcome was serious infection requiring hospitalisation; the secondary outcome was all-cause mortality. The impact of COVID-19 was estimated using an interrupted time-series analysis, with the boundary between April and May 2020 as the change point, following the first declaration of a state of emergency in Japan. Monthly incidence rates were modelled using segmented Poisson regression. Rate ratios (RRs) for level and slope changes with 95% CI were reported. Several sensitivity analyses were performed. Results: Among 1064 patients, total follow-up was 37,535 person-months; 205 serious infections and 96 deaths occurred. For serious infection, the level-change RR was 0.54 (95% CI: 0.31-0.94) and the slope-change RR was 1.01 (0.98-1.04). For all-cause mortality, the level-change RR was 0.35 (0.12-0.98) and the slope-change RR was 1.001 (0.94-1.06). Findings were robust across sensitivity analyses. Conclusions: Immediately after the onset of the COVID-19 pandemic, a clear reduction in serious infections and mortality was observed without major changes in patient characteristics. These findings may reflect the impact of social and personal infection control measures.