Mumps disease in Beijing in the era of two-dose vaccination policy, 2005-2016

Background: Since the introduction of mumps-containing vaccines (MuCV) in 1995 in Beijing, two-dose MuCV vaccination policy has been used, with the 1st and 2nd doses given at 18 months and 6 years of age, respectively.

Methods: Mumps epidemiology during 2005-2016 was described using surveillance data. Vaccine effectiveness (VE) of MuCV against disease was estimated for cases born during 2002-2009 and reported in 2016. VE against complications was estimated for all cases. MuCV coverage was estimated for children born during 1999-2015 using data from Beijing Immunization Information System.

Results: Overall mumps incidence decreased from 30.38/100,000 persons in 2005 to 10.26/100,000 persons in 2016. Incidence declines in children aged <15 years. No significant incidence change occurred in adults aged ≥20 years. Incidence in persons aged 15-19 years increased by 132.73% in 2012 when compared with in 2005. Rates of meningitis/encephalitis, orchitis, and other complications among cases decreased during 2005-2016. The majority (97%) of outbreaks occurred in schools. Total number of outbreaks and average outbreak size decreased during 2005-2016. Among outbreak-related cases, 69.54%, 29.67% and 0.79% had received 0 dose, 1dose and 2 doses of MuCV, respectively. Coverage of the 1st MuCV dose at 2-5 years of age increased by 42.75% during 2005-2016. Coverage of the 2nd MuCV dose at 6-14 years of age increased by 12.87% during 2013-2016. Overall VE estimates of MuCV against mumps disease were 74.51% (95% CI: 65.57-81.34%) for 1 dose and 83.16% (95% CI: 78.60-86.31%) for 2 doses. Both VE estimates increased by birth cohorts. VE estimate against complications for 2-dose MuCV was higher than for 1 dose.

Conclusions: Increasing MuCV coverage achieved declining mumps incidence and complication rate. Current epidemiology supported 2-dose MuCV vaccination policy. The incidence rise in persons aged 15-19 years in 2012 and waning immunity for the 2nd MuCV dose merited close follow-up.