Impact of different MMR vaccination strategies on mumps incidence in Jiangsu, China: A 20-year interrupted time series analysis based on 180,000 cases.

BACKGROUND: Although China upgraded its mumps vaccine schedule to two doses, quantitative evaluations of real-world, population-level effects remain limited. This study systematically evaluated the immediate and long-term impacts of 1-dose and 2-dose measles-mumps-rubella (MMR) vaccination strategies on mumps incidence in Jiangsu Province. METHODS: Statutory infectious disease surveillance data spanning 240 months from 2005 to 2024 in Jiangsu Province (183,490 cases) were collected. An interrupted time series (ITS) analysis was conducted using a generalized linear model (GLM) based on a negative binomial distribution. We evaluated the intervention effects of the vaccine policies while strictly controlling for autoregression, non-linear effects of meteorological factors, population dynamics, and the intensity of COVID-19 non-pharmaceutical interventions (NPIs). Stratified analyses by age group and geographical region were also performed. RESULTS: Following the introduction of the 1-dose MMR policy in 2008, no significant long-term downward trend in mumps incidence was observed across the province (IRR = 1.002, P = 0.773), and periodic outbreaks every 3 to 5 years persisted. Following the comprehensive implementation of the 2-dose MMR strategy in July 2020, the overall incidence exhibited a significant accelerated downward trend of 1.0% per month (IRR = 0.990, P = 0.019). Subgroup analyses revealed that the most heavily burdened 5-9 and 10-14 age groups experienced the most significant long-term declines (1.0% and 1.5% per month, respectively). Furthermore, the ≥15 years adult group, which was not directly targeted for vaccination, also showed a long-term reduction (0.9% per month), indicating a significant herd immunity effect. Additionally, the 2-dose policy successfully smoothed out regional incidence disparities, notably mitigating the compensatory outbreaks observed in Northern Jiangsu in 2019. CONCLUSION: A 1-dose MMR immunization schedule is insufficient to interrupt periodic mumps outbreaks, and the transition to a 2-dose strategy was associated with a steady long-term decline in overall mumps incidence across Jiangsu Province, providing valuable real-world evidence to support the continuation and optimization of 2-dose MMR immunization schedules.