[Reported incidence trend of hand, foot and mouth disease in Hebei Province, 2008-2024: a study based on interrupted time series analysis].

Objective: To analyze the epidemiological characteristics of hand, foot and mouth disease (HFMD) in Hebei Province from 2008 to 2024, and quantitatively evaluate the impacts of enterovirus A71 (EV-A71) vaccination and non-pharmaceutical interventions (NPIs) during the COVID-19 pandemic period on the incidence trend of HFMD by using the interrupted time series (ITS) method. Methods: The incidence data of HFMD in Hebei from 2008 to 2024 were collected for a descriptive analysis to understand the temporal, population, and regional distributions of HFMD. ITS model was used to quantitatively evaluate the impact of EV-A71 vaccination and the NPIs during the COVID-19 pandemic period on HFMD incidence. Additionally, the children under five years old were divided into two age groups (<2 years and ≥2 years) for subgroup ITS analyses to compare the differential responses of age groups to these interventions. Results: A total of 822 740 HFMD cases were reported in Hebei during the study period, the reported cases increased firstly, then-declined, showing an obvious seasonality, with an uneven geographic distribution. The majority of cases were children aged 0-5 years, especially the scattered children, and the incidence rate was higher in boys than in girls. ITS analysis showed that following the introduction of EV-A71 vaccination in 2016, the annual decline in overall HFMD incidence accelerated from 2.00 per 100 000 (P=0.735) to 10.67 per 100 000 (P=0.186). Age-stratified analysis indicated that in children under 2 years old, HFMD incidence trend reversed from increase to decrease (P=0.014). In children aged ≥2 years, the incidence remained generally stable before and after the vaccination, with no significant immediate or long-term changes observed. In 2020, when COVID-19 control measures were taken, HFMD incidence significantly decreased in both overall population and the two age groups, with a greater decline observed in children aged ≥2 years compared with those aged <2 years. Subsequently, the incidences in both groups showed rebounds. Conclusions: From 2008 to 2024, the HFMD incidence in Hebei exhibited distinct phase-specific changes, resulting from the synergistic effects of pathogen spectrum shifts, vaccine interventions, and public health measures. Following the introduction of the EV-A71 vaccine, the incidence of HFMD showed a decreasing trend, but the intervention effect exhibited age heterogeneity, being more significant in children under 2 years old. The NPIs during the COVID-19 pandemic period significantly suppressed HFMD transmission for a short time. These findings suggest that relying solely on overall incidence is insufficient to fully evaluate type-specific vaccine effects; integrating pathogen type surveillance and age-stratified analyses can provide a more accurate evaluation of HFMD control and inform the optimization of comprehensive prevention strategies.