Impact of COVID-19 on the transmission dynamics of HFMD associated enterovirus serotypes in Japan: A modelling study of surveillance data.

A notable decline in incidence of hand, foot, and mouth disease (HFMD) was observed globally since the beginning of the COVID-19 pandemic, indicating a change in the transmission dynamics of enteroviruses (EVs) causing HFMD. This study estimates the impact of COVID-19 non-pharmaceutical interventions (NPIs) on the transmission of EVs in Japan. Japan has a well-established sentinel surveillance system for enteroviruses and HFMD. A susceptible-infected-recovered stochastic transmission model was fitted to the time-series of weekly reported number of HFMD enterovirus A71 (EV-A71), coxsackievirus A16 (CVA16), and CVA6 cases from January 2005 to December 2024, to estimate the impact of government containment interventions during the COVID-19 pandemic. Compared to pre-pandemic levels, the transmission rate decreased by 7.86 % (95 % Credible Interval (CrI): 6.31 %, 10.3 %) for EV-A71, 12.0 % (10.3 %, 14.1 %) for CVA16, and 20.1 % (16.3 %, 24.0 %) for CVA6 on average from January 2020 to December 2022. The reduction in transmission rate during this period correlated with the COVID-19 Stringency Index, such that 49.3 %, 19.9 % and 25.5 % of the reduction for each serotype respectively was explained by the index, with the biggest reductions occurring during "State of Emergency" periods. Enterovirus serotypes with higher transmissibility (R0) and therefore, a younger mean age at infection, were estimated to experience a bigger reduction in transmission that was more strongly associated with COVID-19 non-pharmaceutical interventions captured by the Stringency Index. This has implications for the impact of NPIs on other viral pathogens.