Investigating the characteristics of mumps outbreaks in Fujian Province, China.

OBJECTIVES

Identifying the specifics and potential causes of mumps outbreaks in the Fujian Province during the period of 2017 to 2022.

METHODS

Mumps cases reported by the National Notifiable Communicable Disease Report System (NNCDRS) in China during the observation period of the 5 years were investigated annually and by age to detect homogeneity of the spread of the disease over time. If specific age-peaks may appear, we investigated those figures by analysing group characteristics in mumps cases presented as outbreaks. Those characteristics include demography (age and sex), clinical symptoms, place and time identification, and vaccination status. Regarding the latter, it was hypothesized that cases manifesting an outbreaks and appearing in young adults should have a low vaccination coverage, and a long-lasting period since they received their vaccine.

RESULTS

The total number of mumps cases reported during the observation period was 15,294, leading to incidence rates ranging from 3.2/100,000 to 8.0/100,000 per year. In the older age-group the disease spread by year and age (9 to 15y old) manifested 20 outbreaks accounting for 710 cases, all happening during 2017 to 2019. Thereafter those outbreaks disappeared in that age-group. The group characteristics specified that all the outbreaks happened in school settings, with a median age of 13y (range 6 to 19y). Parotid gland enlargement was observed in 82.7 %. The median duration of the outbreaks was 28 days, varying from 14 to 74 days. Only 27.6 % of the cases received at least one dose of the MuCV vaccine, and among these vaccinated individuals, 94.9 % developed mumps more than 5 years after vaccination. The dramatic reduction in outbreaks after 2019 could be explained by the public health measures taken during the COVID period and/or the new vaccination policy implemented in 2008 (free vaccination, 1 dose) and 2020 (2 doses) of young children causing therefore a lower rate of circulation of the virus.

CONCLUSION

Mumps outbreaks observed in young adults during 2017-2019 causing a disease peak, indicated a potential link to unsatisfactory vaccination coverage with prolonged interval since receiving the vaccine. As those disease peaks disappeared since 2020, close monitoring for new outbreaks in young adults is recommended that may initiate a new vaccination strategy for that age-group.