Objective To investigate the long-term trends of mumps incidence among individuals aged <20 years in Zhuji City, Zhejiang Province from 2009 to 2023, so as to provide data support for formulating scientific prevention and control strategies against mumps.

Methods Epidemiological data on mumps incidence among individuals aged <20 years in Zhuji City from 2009 to 2023 were collected from the National Notifiable Infectious Disease Reporting System of the China Disease Control and Prevention Information System. An age-period-cohort (APC) model was employed to analyze the net drift in incidence rates and the effects of age, period, and birth cohort on mumps incidence.

Results A total of 5 890 cases of mumps were reported among individuals aged <20 years in Zhuji City from 2009 to 2023, with an average annual reported incidence rate of 167.24/100 000. The APC model analysis revealed that the highest incidence of mumps was observed in the 5 to <10 years age group (202.60/100 000). Over the period from 2009 to 2023, the incidence of mumps in Zhuji City showed an overall decline trend, with a net drift of -12.828% (95%CI:-17.406%‒-7.996% ). After adjusting for age and birth cohort effects, the highest risk of mumps incidence was observed between 2009 and 2013 relative risk (RR)=2.146, 95%CI: 1.361‒3.384. After adjusting for age and period effects, the 1994‒1998 birth cohort exhibited the highest risk of mumps incidence (RR=31.849, 95%CI: 5.505‒184.269), followed by 1999‒2003 birth cohort (RR=10.105, 95%CI: 4.496‒22.711) and 2004‒2008 birth cohort (RR=2.758, 95%CI: 1.659‒4.586). No statistically significant difference was observed in the risk of mumps between the 2014‒2018 and 2019‒2023 birth cohorts, with relative risks of 1.311 (95%CI: 0.761‒2.259 ) and 1.228 (95%CI: 0.485‒3.106), respectively.

Conclusion From 2009 to 2023, the incidence of mumps among individuals aged <20 years in Zhuji City showed an overall downward trend, with statistically significant differences observed across age groups, time periods, and birth cohorts. Based upon the existing national immunization strategy, priorities should be given to enhance surveillance and interventions for school-aged children aged 5‒<10 years.