Multi‐inflammatory syndrome and Kawasaki disease in children during the COVID‐19 pandemic: A nationwide register‐based study and time series analysis

AIM: We investigated whether the ongoing COVID‐19 pandemic was associated with the occurrence of Kawasaki disease or with multi‐inflammatory syndrome in children (MIS‐C). METHODS: This national Finnish register‐based study was based on laboratory‐confirmed severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infections, MIS‐C and Kawasaki disease cases. We performed a time series analysis on the occurrence of Kawasaki disease in 2016–2020. RESULTS: In 2020, there were 5170 laboratory‐confirmed COVID‐19 cases in children under 18 years of age and five fulfilled the MIS‐C case definition. The occurrence of MIS‐C was 0.97 per 1000 (95% confidence interval: 0.31‐2.26) laboratory‐confirmed SARS‐CoV‐2 infections in children. Our time series analysis showed that Kawasaki disease cases decreased during the COVID‐19 pandemic. The seasonally adjusted incidence rate ratio was 0.49 (95% confidence interval: 0.32‐0.74) when it was compared to pre‐pandemic levels. This coincided with a reduced occurrence of respiratory infections, due to social distancing in the population. CONCLUSION: This nationwide register‐based study found that MIS‐C was a rare complication of the SARS‐CoV‐2 infection. The occurrence of Kawasaki disease and respiratory infections decreased during the pandemic. This suggests that transmissible microbes may play an important role in Kawasaki disease and social distancing may have a protective effect.