To investigate the impacts of different vaccination doses and intervals on the age of onset in mumps-containing vaccine (MuCV) breakthrough cases, providing evidence for optimizing MuCV immunization strategies.

Data were matched from the China Disease Prevention and Control Information System and the Chongqing Immunization Planning Information Management System. MuCV breakthrough cases in children born in Shapingba district between January 1, 2008 and December 31, 2023, who received MuCV and were diagnosed with mumps by December 31, 2023, were included. A multivariate linear regression model was employed to analyze the effects of vaccination doses and intervals on the age of onset in breakthrough cases.

From 2008 to 2023, 1 204 MuCV breakthrough cases were identified in Shapingba district, with disease onset primarily occurring in children aged 1–9 years (5–9 years: 639 cases, 53.07%). Breakthrough cases occurred in 782 (64.95%), 418 (34.72%), and 4 (0.33%) children who had received 1, 2, and 3 doses of MuCV, respectively, with mean onset ages of (5.25 ± 2.12), (6.52 ± 2.07), and (7.81 ± 2.51) years. Among children receiving 2 doses, those with intervals of < 2 years (97 cases, 23.21%), 2–4 years (193 cases, 46.17%), and > 4 years (128 cases, 30.62%) between doses had mean onset ages of (4.92 ± 2.08), (6.27 ± 1.53), and (8.10 ± 1.64) years, respectively. Significant differences in mean age of onset were observed across different vaccination doses and intervals (all P < 0.001). After adjusting for gender, residence, and household registration, multivariate regression showed that 2-dose (β = 1.275, 95%CI: 1.024–1.525) and 3-dose (β = 2.581, 95%CI: 0.510–4.652) recipients had delayed ages of onset compared with 1-dose recipients, with a linear trend between increasing doses and delayed onset (β = 1.275, P < 0.001). For the second dose, intervals of 2–4 years (β = 1.324, 95%CI: 0.909–1.738) and > 4 years (β = 3.175, 95%CI: 2.726–3.624) delayed onset compared with intervals < 2 years, with a linear trend between prolonged intervals and delayed onset (β = 1.605, P < 0.001).

MuCV breakthrough cases in Shapingba district from 2008 to 2023 predominantly occurred in children aged 5–9 years. Increasing vaccination doses and extending the interval to the second dose significantly delayed the age of onset.