Impacts of two-dose mumps-containing vaccine strategy on mumps incidence using segmented regression models.

OBJECTIVES

To evaluate the impact of China's two-dose measles-mumps-rubella (MMR) vaccination strategy on mumps incidence using interrupted time series (ITS) analysis in a megacity of China from 2004 to 2024.

METHODS

Monthly reported mumps case data were extracted from China's National Mandatory Disease Reporting System (NNDRS). Segmented regression models assessed policy effects across three periods: pre-vaccine during 2004-2007, one-dose MMR during 2008 to 2020, and two-dose MMR during 2020-2024. The Newey-West correction is used to address autocorrelation issue (P < 0.01 for Durbin-Watson test).

RESULTS

Adolescents aged 10-15 years have the highest reported mumps cases across all the years, but with lower case peaks since the two-dose MMR schedule in 2020. ITS analysis revealed a significant downward trend after the two-dose MMR vaccination schedule with a slope change of -0.007 (P < 0.01) and an immediate reduction in cases with a level change of -0.256 (P = 0.056) on log-transformed value. The two-dose MMR policy generated a cumulative effect of reducing 53.76 % mumps morbidity on December 2024 compared to the one-dose policy. Age-specific incidence peaks have been shifted, with adolescents aged 10-15 years remaining to be highest-risk despite vaccination, and breakthrough infections persisted in highly vaccinated school populations.

CONCLUSIONS

The two-dose MMR strategy significantly reduced mumps incidence in the city, supporting its effectiveness for epidemic control. However, persistent cases in adolescents propose consideration of school-based booster programs and enhanced surveillance for emerging strains.