Seasonal Variation in Antineutrophil Cytoplasmic Antibody (ANCA)-Associated Vasculitis Onset Before and During the Coronavirus Disease 2019 (COVID-19) Pandemic: Findings From the Multicenter J-CANVAS Registry.
Oka N, Yoshida Y, et al. • International journal of rheumatic diseases • 2026
AAV exhibited a clear seasonal pattern, which differed during the COVID-19 period, with seasonal variation consistently observed in MPA but not in GPA and EGPA.
Key Findings
Results
ANCA-associated vasculitis onset showed significant seasonal variation in the pre-COVID-19 period, with lower onset in autumn and higher onset in spring and summer compared to winter.
Poisson regression analysis revealed a seasonal variation in AAV onset in the pre-COVID-19 period (p < 0.001)
Autumn had lower incidence rate ratio (IRR 0.64, p < 0.001) compared to winter
Spring had higher onset (IRR 1.16, p = 0.048) compared to winter
Summer had higher onset (IRR 1.23, p = 0.005) compared to winter
Analysis was based on 499 patients newly diagnosed in the pre-COVID-19 period (2017–2019)
Results
The seasonal pattern of AAV onset differed significantly between the pre-COVID-19 and COVID-19 periods, with a relative increase in spring onset during the COVID-19 period.
A significant interaction between season and period was identified (p for interaction = 0.032)
There was a relative increase in spring onset during the COVID-19 period (IRR 1.16, p = 0.010)
The COVID-19 period included 372 newly diagnosed patients (2020–2022)
Total study population was 871 patients across both periods
Results
Seasonal variation in AAV onset was consistently observed in microscopic polyangiitis (MPA) but not in granulomatosis with polyangiitis (GPA) or eosinophilic granulomatosis with polyangiitis (EGPA).
Subanalyses were performed separately for MPA, GPA, and EGPA disease subtypes
MPA showed consistent seasonal variation across analyses
GPA and EGPA did not demonstrate statistically significant seasonal variation
The interaction between season and period was not statistically significant in each individual disease group
Methods
The study was a retrospective cohort study using a nationwide multicenter Japanese registry (J-CANVAS) of patients newly diagnosed with AAV between 2017 and 2022.
Data were drawn from the J-CANVAS (Japan-CANVAS) multicenter registry
Study included patients with MPA, GPA, and EGPA
Total of 871 patients were included: 499 in pre-COVID-19 period and 372 in COVID-19 period
The pre-COVID-19 period was defined as 2017–2019 and the COVID-19 period as 2020–2022
Poisson regression was the primary statistical method for analyzing seasonal distribution
Discussion
The factors underlying the differences in seasonal patterns between the pre-COVID-19 and COVID-19 periods remain unclear and were not consistently observed across individual disease subtypes.
Authors stated that 'these differences were not consistently observed across individual disease subtypes, and the factors underlying them remain unclear'
No specific environmental, infectious, or behavioral explanatory factors were confirmed in this study
The study design was retrospective, limiting causal inference
What This Means
This research suggests that the timing of new diagnoses of ANCA-associated vasculitis (AAV) — a group of rare diseases where the immune system attacks blood vessels — follows a seasonal pattern in Japan. Using data from 871 patients diagnosed between 2017 and 2022, researchers found that before the COVID-19 pandemic, more cases tended to be diagnosed in spring and summer, and fewer in autumn, compared to winter. This pattern was particularly consistent for the subtype called microscopic polyangiitis (MPA), but not for the other subtypes (GPA and EGPA).
This research also suggests that the seasonal pattern shifted during the COVID-19 pandemic years (2020–2022), with a statistically significant interaction indicating the distribution across seasons was different compared to the pre-pandemic period — specifically, there appeared to be a relative increase in spring-onset cases during the pandemic. However, when each disease subtype was analyzed separately, this difference was not statistically significant in any individual group, making the finding harder to interpret.
The practical significance of these findings is that environmental or behavioral factors tied to seasons — potentially including respiratory infections, temperature, or lifestyle changes during the pandemic — may play a role in triggering AAV. However, the study cannot determine what those factors are, and the inconsistency across disease subtypes means caution is needed in drawing firm conclusions. Further research would be needed to understand why these seasonal patterns exist and why they may have changed during the pandemic.
Oka N, Yoshida Y, Kidoguchi G, Fujii M, Kobayashi H, Hosokawa Y, et al.. (2026). Seasonal Variation in Antineutrophil Cytoplasmic Antibody (ANCA)-Associated Vasculitis Onset Before and During the Coronavirus Disease 2019 (COVID-19) Pandemic: Findings From the Multicenter J-CANVAS Registry.. International journal of rheumatic diseases. https://doi.org/10.1111/1756-185x.70878