Nonpharmaceutical interventions (NPI) implemented during the COVID-19 pandemic reduced the incidence of Kawasaki disease (KD), according to findings from a research letter published in Circulation. These findings may provide insight into the pathogenesis of KD.

The widespread implementation of NPIs during the pandemic provided a unique opportunity to assess their impact on other diseases, including COVID-19.

To identify whether NPIs were associated with a change in KD incidence, the study authors conducted a retrospective, ecologic study on all KD cases in South Korea between January 2010 and September 2020. Data were extracted from the National Health Insurance Service database. The NPI period was defined as February through September 2020, during which NPIs were widely implemented in South Korea. The KD incidence rate during this period was compared with mean incidence rates during the same months of the prior years (pre-NPI). Cases of KD were defined by the simultaneous presence of 2 International Statistical Classification of Diseases, Tenth Revision (ICD-10) codes: the disease code for KD and the prescription code for intravenous immunoglobulin (IVIg). IVIg-resistant KD was defined as persistent fever 24 to 48 hours after the first IVIg infusion, requiring subsequent IVIg prescriptions for at least 3 days. An autoregressive integrated moving average model was used to characterize changes in KD incidence during the study period.

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A total of 53,424 cases of KD were identified between 2010 and 2020. The majority of cases (83%) occurred in children aged younger than 5 years; 17% were resistant to treatment with IVIg. In the pre-NPI period, the annual mean incidence of KD was 48.1 per 100,000 persons; the mean monthly incidence was 4.1 per 100,000 persons. The incidence of KD sharply declined following NPI implementation in March 2020; however, from April 2020 onward, these rates plateaued. The overall incidence of KD during the NPI period was 18.8 per 100,000 persons, which was significantly lesser than the mean value of 31.5 per 100,000 persons calculated for the same months during the prior years.

The incidence among children aged between 0 and 4 years during the NPI period was 80.0 per 100,000 persons. In the prior years, this rate was estimated at 123.0 per 100,000 persons (P =.003). The incidence among children aged between 5 and 9 years was also significantly lower during the NPI period compared with the prior years (10.6 vs 23.8 per 100,000 persons; P =.04). The implementation of NPIs did not appear to significantly impact the incidence rates among children aged between 10 and 19 years. The incidence of IVIg-resistant KD also did not change significantly during the NPI period compared with the average incidence during the previous 10 years. However, the authors noted that the overall rate of IVIg-resistant KD has been increasing since 2018 and no commensurate increase was observed following NPI implementation.

Findings from this analysis suggested that interventions developed during the COVID-19 pandemic also impacted the incidence of KD; however, the reasons for this association are still unclear. Authors noted that the incidence of febrile diseases, often confused with KD, also decreased during the NPI period, which may have created a bias.

“Further long-term research is needed to determine whether the decrease in incidence of KD is solely attributable to the effects of NPI,” the authors wrote.


Kang J-M, Kim Y-E, Huh K, et al. Reduction in Kawasaki disease after nonpharmaceutical interventions in the COVID-19 era: a nationwide observational study in Korea. Circulation. 2021;143(25):2508-2510. doi:10.1161/CIRCULATIONAHA.121.054785