Mumps - Annual Epidemiological Report 2016 [2014 data]

Key facts

• In 2014, 11 069 cases of mumps were reported to TESSy.
• The notification rate was 2.5 cases per 100 000 population, less than half the notification rate observed in 2012 and 2013.
• Young children and adolescents were the most affected age groups.
• The majority of cases were vaccinated, a third with two or more doses.
• The current epidemiology of mumps in Europe may be largely explained by waning immunity and a growing susceptible population.
• High vaccination coverage is of paramount importance to prevent mumps outbreaks.

Methods

Click here for a detailed description of the methods used to produce this annual report

ECDC has coordinated the surveillance of mumps at the European level since the transfer of EUVAC.NET (European surveillance network for selected vaccine-preventable diseases, hosted by Statens Serum Institute, Denmark) to ECDC in 2011.

• In 2014, 28 EU/EEA Member States routinely reported mumps data to TESSy.
• The majority of Member States reported data on mumps in accordance with the 2008 or 2012 EU case definition (Commission Implementing Decision 2012/506/EU of 8 August 2012 of the European Parliament and of the Council).
• The majority of Member States reported data from comprehensive, passive surveillance systems with national coverage. For a summary of the surveillance systems characteristics in each Member State, please refer to the Annex.

Epidemiology

In 2014, 28 EU/EEA countries provided mumps surveillance data. In total, 11 069 cases of mumps were reported, of which 5 342 (48%) were laboratory-confirmed. Iceland reported zero cases, while Austria, France and Lichtenstein did not report data. The notification rate of confirmed cases was 2.5 per 100 000 population, less than half the notification rate observed in 2012 (5.4) and 2013 (5.9) (Table 1 and Figure 1).

Slovakia reported the highest notification rate (28.8 cases per 100 000), followed by Ireland (16.0), Poland (6.6) and the Czech Republic (6.4) (Table 1 and Figure 2).

Since 2013, notable increases in the notification rate were observed in Slovakia (4.0 cases per 100 000 in 2013 to 28.8 cases per 100 000 in 2014) and Ireland (4.8 in 2013 to 16.0 in 2014). A substantial decrease in the notification rate was reported by Belgium (40.8 in 2013 to 2.0 in 2014), following a large outbreak in 2012–2013 for which mandatory reporting was introduced [1]. Notable decreases were also observed in the Czech Republic (14.8 in 2013 to 6.4 in 2014) and Spain (12.4 in 2013 to 2.2 in 2014) (Table 1).

Age and gender distribution

In 2014, the most affected age group were the 5–9-year-olds, with a notification rate of 9.0 cases per 100 000 population (Figure 3). This was the most affected age group in the majority of Member States, particularly Slovakia (165.6 cases per 100 000 population) and Poland (44.3). Slovakia also reported high rates among 10–14- (153.5) and 15–19-year-olds (97.7). The second highest notification rate in Europe was observed among 15–19-year-olds  (8.2 cases per 100 000), followed by 1–4- (6.4) and 10–14-year-olds (6.4). Fifteen-to-nineteen-year-olds were the most affected age group in the Czech Republic, Ireland, Malta and the United Kingdom. In Ireland, 87% of cases were aged 15 years or older. Males (2.8 cases per 100 000 population) were more often affected than females (2.2 per 100 000) in all age groups, with a male-to-female ratio of 1.3:1.

Seasonality

In 2014, the highest number of cases was reported at the end of the year and in early spring, whereas the lowest numbers were reported during summer and early autumn (Figures 4 and 5). In previous years, a peak of reported mumps cases was usually seen in early spring. This seasonality is compatible with the known epidemiology of mumps. The peak in early spring was driven by a higher number of cases reported by the United Kingdom (414 cases in April 2014), whereas the winter peak was predominantly due to increases in the number of cases reported by Ireland and Slovakia (200 and 284 cases reported in December 2014, respectively).

Vaccination status

Data on vaccination status were available for 9 305 cases (84%). Of these 9 305 cases, 3 066 (33%) were unvaccinated, 2 634 (28%) were vaccinated with one dose, 3 055 (33%) with two doses, and 50 (0.5%) with three or more doses. Five hundred cases (5%) had been vaccinated with an unknown number of doses. Among laboratory-confirmed cases, 47% were unvaccinated, compared to 15% and 25% of probable and possible cases, respectively.

Outcome

Outcome was known for 6 227 cases, 56% of all cases. No deaths were reported in 2014.

Hospitalisation and complications

Of 5 031 cases with known hospitalisation status, 398 (8%) were hospitalised. Data on complications were reported in 3 118 cases, of which 2 830 (90%) had no complication. There were 117 cases of orchitis, 28 cases of pancreatitis, 18 cases of meningitis and three cases of encephalitis. Two cases were complicated with both meningitis and orchitis. Unspecified complications (‘other’) were reported for another 120 cases. Complications were more frequently reported in adolescents and young adults than in children.

Discussion

In 2014, the notification rate of mumps cases was less than half the notification rate observed in 2012 and 2013. This was predominantly driven by a decrease in the number of cases reported by Belgium and Spain. The decrease in Belgium is likely to be due to a switch back to a sentinel surveillance system from mandatory reporting at the end of 2013. Mandatory notification was introduced in 2012 because of a large outbreak. Some Member States, such as Ireland and Slovakia, did report notable increases in the number of cases. The highest age-specific notification rates in Europe were observed in 5–9- and 15–19-year-olds, although the most affected age groups differed between Member States. Several factors may explain the observed differences in the epidemiology between Member States, including differences in surveillance systems, historical or current vaccination policies, and vaccination coverage levels.

The fact that all EU/EEA Member States have added mumps vaccination to their routine childhood immunisation schedules has significantly reduced the associated disease burden compared to the pre-vaccine period. However, of the mumps cases in Europe in 2014 for which vaccination status was known, the majority were vaccinated, a third of them with at least two doses. Several outbreaks in populations with high vaccination coverage have occurred in recent times, particularly among populations of teenagers and young adults, both in Europe and around the world [1-5]. This may be due to waning immunity in the absence of natural boosting. Studies have shown that the time between the first and second dose [6] and the time after vaccination [1] may play a role in susceptibility to mumps infection, while the immunogenicity and effectiveness varies according to the vaccine strain [7,8]. Also, social conditions that facilitate intense exposure, for example in universities, may increase the transmission of the virus [1,3,5].

Low vaccination coverage may also play a role, as it is associated with a higher risk of mumps outbreaks [6,9], while the risk of complications following mumps infection is lower in previously vaccinated persons than in non-vaccinated individuals [10,11]. In Europe, data are consistent with the understanding that complications are more frequently reported in adolescents and young adults than in children [12].

Public health conclusions

Further research into waning immunity to mumps virus is needed in order to improve future immunisation programmes. Meanwhile, maintaining a high coverage with two doses of measles, mumps and rubella (MMR) vaccine is of paramount importance to prevent mumps outbreaks. Revaccination of adolescents and young adults may be considered to increase vaccination coverage and combat waning immunity, particularly among those who received less than two doses of the vaccine during childhood [6]. The protective effect of vaccination on disease severity is critical and should be considered in current and future mumps prevention and control strategies.

Since all European countries use MMR vaccines in their national childhood immunisation programmes, mumps prevention benefits indirectly from the efforts made to reach the goal of eliminating measles and rubella in Europe.

References

1. Braeye T, Linina I, De Roy R, Hutse V, Wauters M, Cox P, et al. Mumps increase in Flanders, Belgium, 2012–2013: results from temporary mandatory notification and a cohort study among university students. Vaccine. 2014;32(35):4393-8.
2. Cordeiro E, Ferreira M, Rodrigues F, Palminha P, Vinagre E, Pimentel JP. Mumps outbreak among highly vaccinated teenagers and children in the central region of Portugal, 2012–2013. Acta Med Port. 2015;28(4):435-41.
3. Park SH. Resurgence of mumps in Korea. Infect Chemother. 2015;47(1):1-11.
4. Limberkova R, Lexova P. [Genotyping results, laboratory diagnosis, and epidemiology of the mumps virus circulating in the Czech Republic in 2012]. Epidemiol Mikrobiol Imunol. 2014;63(1):36-42.
5. Dayan GH, Quinlisk MP, Parker AA, Barskey AE, Harris ML, Schwartz JM, et al. Recent resurgence of mumps in the United States. N Engl J Med. 2008;358(15):1580-9.
6. Eriksen J, Davidkin I, Kafatos G, Andrews N, Barbara C, Cohen D, et al. Seroepidemiology of mumps in Europe (1996–2008): why do outbreaks occur in highly vaccinated populations? Epidemiol Infect. 2013;141(3):651-66.
7. Galazka AM, Robertson SE, Kraigher A. Mumps and mumps vaccine: a global review. Bull World Health Organ. 1999;77(1):3-14.
8. Dayan GH, Rubin S. Mumps outbreaks in vaccinated populations: are available mumps vaccines effective enough to prevent outbreaks? Clin Infect Dis. 2008;47(11):1458-67.
9. Vandermeulen C, Leroux-Roels G, Hoppenbrouwers K. Mumps outbreaks in highly vaccinated populations: What makes good even better? Hum Vaccin. 2009;5(7):494-6.
10. Zamir CS, Schroeder H, Shoob H, Abramson N, Zentner G. Characteristics of a large mumps outbreak: Clinical severity, complications and association with vaccination status of mumps outbreak cases. Hum Vaccin Immunother. 2015;11(6):1413-7.
11. Yung CF, Andrews N, Bukasa A, Brown KE, Ramsay M. Mumps complications and effects of mumps vaccination, England and Wales, 2002–2006. Emerg Infect Dis. 2011;17(4):661-7; quiz 766.
12. Mumps virus vaccines. Wkly Epidemiol Rec. 2007;82(7):51-60.