[Effects of the MMR vaccination on the epidemiology of mumps in Germany]

Mumps in the Vaccination Age: Global Epidemiology and the Situation in Germany

Vaccination against mumps virus (MuV) (mostly measles-mumps-rubella) is routinely performed in more than 120 countries and has resulted in a distinct decrease of mumps incidence. However, alteration of mumps epidemiology has been observed in several countries after implementation of the vaccine but is sparsely documented. Moreover, outbreaks have occurred after starting vaccination, even in highly vaccinated populations. In the former German Democratic Republic (DDR) mumps was a notifiable disease but vaccination against mumps was not implemented. In the five eastern German states forming the DDR until 1990, mumps was not notifiable until 2001. Except for the lack of reporting between 1990–2000, data from Eastern Germany allow analysis of mumps epidemiology after initiating the vaccination campaign. For the period from 2001 to 2016 the data show that the incidence of mumps dropped notably after initiating vaccines, and was accompanied by an increase of the median age of patients with mumps. In Eastern Germany, no outbreaks were noted, while several outbreaks occurred in Western Germany, possibly due to a lower vaccination rate. Further literature analysis revealed that outbreaks were facilitated by waning immunity and crowding. Nevertheless, although vaccination prevented infection, the course of illness, once infected, was sometimes more complicated. In comparison to non-vaccinated populations, high rates of complicated courses occurred and were marked by orchitis, due to higher age of mumps patients. Therefore, refusing vaccination against mumps increases the risk of severe courses when living in a vaccinated population.

Laboratory-based investigation of suspected mumps cases submitted to the German National Reference Centre for Measles, Mumps, and Rubella, 2008 to 2013

From 2008 to 2013, sample sets from 534 patients displaying clinical symptoms of mumps were submitted to the German Reference Centre for Measles, Mumps and Rubella. Mumps virus infection was confirmed in 216 cases (40%) by PCR and/or serology. Confirmed cases were more frequently seen in male than in female patients (128 vs. 81); the age group predominantly affected was 15 to 29 years old (65%, median age: 26.4 years). The majority of the confirmed cases had a remote history of vaccination with one or two doses of a mumps-containing vaccine (69%). Our results indicate that mumps virus caused two outbreaks in Bavaria in 2008 and 2010/2011 and a third one in Lower Saxony in 2011. Mumps virus genotype G was preponderantly detected from 2008 to 2013. For 107 of the 216 patients with a confirmed mumps infection, we correlated the results from PCR and serology. PCR detected cases during the first week after onset of symptoms (74% positive results). PCR worked best with throat swabs and oral fluids (61% and 60% positive results, respectively). IgM was more reliable with a longer time after onset of symptoms (67%), but indirect IgM serology was of insufficient sensitivity for vaccinated mumps cases (30%); the IgM μ-capture assay detected more cases in this group. Mumps virus is able to initiate an infection in vaccinated patients (secondary vaccine failure, SVF) although it is unclear to what extent. Since SVF does occur in highly vaccinated populations and IgM will not increase to detectable levels in all SVF patients, we strongly recommend using PCR plus serology tests to avoid false-negative diagnoses in vaccinated individuals with clinical signs of mumps.

Outbreak-related mumps vaccine effectiveness among a cohort of children and of young adults in Germany 2011

Mumps outbreaks in populations with high 2-dose vaccination coverage and among young adults are increasingly reported. However, data on the duration of vaccine-induced protection conferred by mumps vaccines are scarce. As part of a supra-regional outbreak in Germany 2010/11, we conducted two retrospective cohort studies in a primary school and among adult ice hockey teams to determine mumps vaccine effectiveness (VE). Via questionnaires we collected information on demography, clinical manifestations, and reviewed vaccination cards. We estimated VE as 1-RR, RR being the rate ratio of disease among two-times or one-time mumps-vaccinated compared with unvaccinated persons. The response rate was 92.6% (100/108--children cohort) and 91.7% (44/48--adult cohort). Fourteen cases were identified in the children and 6 in the adult cohort. In the children cohort (mean age: 9 y), 2-dose VE was 91.9% (95% CI 81.0-96.5%). In the adult cohort (mean age: 26 y), no cases occurred among the 13 2-times vaccinated, while 1-dose VE was 50.0% (95% CI -9.4-87.1%). Average time since last vaccination showed no significant difference for cases and non-cases, but cases were younger at age of last mumps vaccination (children cohort: 2 vs. 3 y, P=0.04; adult cohort: 1 vs. 4 y, P=0.03). We did not observe signs of waning immunity in the children cohort. Due to the small sample size VE in the adult cohort should be interpreted with caution. Given the estimated VE, very high 2-dose vaccination coverage is required to prevent future outbreaks. Intervention efforts to increase coverage must especially target young adults who received<2 vaccinations during childhood.