The effect of mumps vaccine on the incidence of mumps in Hefei: An interrupted time-series analysis.

To quantitatively assess the incremental protective effect of two-dose mumps vaccination in Hefei. Monthly mumps incidence during 2011-2023 were collected. The Interrupted Time Series and Segmented Regression Analyses (ITSA) were employed to evaluate the variations in monthly mumps incidence following the introduction of one-dose mumps-containing vaccine (MuCV) and two-dose measles-mumps-rubella combined attenuated live vaccine (MMR) into the Expanded Program on Immunization (EPI). The average annual incidence was 16.95 per 100,000 population (18.75 and 10.95 in one-dose and two-dose vaccination periods respectively). The incidence was the highest among children aged 5-14. ITSA revealed that monthly incidences of mumps decreased by 0.015 per 100,000 (β = -0.015, < .001) in one-dose MuCV vaccination period. The incidence decreased in all four age groups, with the largest decline observed among children aged 10-14 (β = -0.139, < .001), followed by children aged 5-9 (β = -0.089,  = .003). In two-dose MMR vaccination period, the monthly incidence of total population, 0-4, 5-9, 10-14 and ≥15 average decreased by 0.014, 0.109, 0.133, 0.018, and 0.0003 (β+β) per 100,000, respectively. The mumps incidence decreased over time with the highest annual incidence shifting to young children. One-dose MuCV vaccination significantly reduced the incidence of mumps, with the largest decline observed among children aged 5-14, but the effect diminishes in older age groups. Booster vaccination for adolescents over 10 years old or optimizing the dose interval might be a good option to effectively control the incidence of mumps. The impact of the two-dose MMR immunization strategy on the trend of mumps morbidity necessitates additional investigation.