Outbreak of mumps in a student population with high vaccination coverage in China: time for two-dose vaccination

ABSTRACT

In 2016, an outbreak of mumps occurred in a primary school in China with a student population having high vaccination coverage. An unmatched case-control study was performed to identify risk factors contributing to this outbreak, and a retrospective cohort study was conducted to evaluate the effectiveness of mumps-containing vaccine (MuCV). A total of 97 cases were identified during the outbreak, and the overall attack rate was 8.2%. Among students with confirmed vaccination status, 90% had received at least one dose of MuCV. Cases were more likely than non-cases to report taking the school bus during the epidemic period (adjusted OR = 2.3, 95% CI: 1.4–3.7). Vaccine effectiveness (VE) was higher for two-dose MuCV (76%, 95% CI:49–89%) than for one-dose MuCV (59%, 95% CI: 36–74%. The protection afforded by both one-dose and two-dose MuCV waned over time, from 82% among students vaccinated within 5 years to 41% among those vaccinated more than 10 years previously for one-dose VE, and from 90% to 25% over the same time period for two-dose VE. We found that outbreaks of mumps can occur in schools despite high coverage of one-dose MuCV vaccination. Although the VE of both two-dose and one-dose MuCV wanes over time, the overall VE for two-dose MuCV was superior than that of one-dose MuCV. Therefore, a two-dose MuCV schedule through routine services is likely needed in order to control mumps epidemics in China.

KEYWORDS:

• Mumps
• vaccine effectiveness
• risk factors
• outbreak

Acknowledgments

We would like to acknowledge the contributions of all of the participants in the outbreak investigation, especially public health workers from the Jin’an CDC and Zhongdian Township Health Hospital. Many thanks for the support from the Field Epidemiology Training Program of the China CDC.

Disclosure of potential conflicts of interest

No potential conflicts of interest were disclosed.

Authors’ contributions

Wei QIN and Yao WANG participated in the data analysis and drafted the manuscript. Hong SU critically reviewed and supervised development of the paper. Shao-yu XIE, Kai-chun LI, and Wei QIN designed the retrospective cohort study and the questionnaire. Tao YANG, Xiao-kang XU, Xiang-mei MENG, Chang-jun ZHAO, and Shao-yi LI performed the field epidemiological investigation. All of the authors contributed to the review and revision of the final manuscript.

Ethical considerations

Ethical clearance was not required as this outbreak investigation was urgent and considered to be a public health response.