Mumps outbreaks across England and Wales in 2004: observational study

Introduction

In October 1988, routine immunisation against mumps was introduced in the United Kingdom as a combined measles, mumps, and rubella (MMR) vaccine for children aged 12-15 months. Although the incidence of mumps declined quickly, mathematical modelling supported the introduction of a second dose of MMR in 1996.1 In 1999, numbers of cases of mumps in teenagers in England and Wales began to rise. We report a further increase in the incidence of mumps in 2004.

Participants, methods, and results

Notifications of clinically diagnosed and laboratory confirmed mumps cases are collated for England and Wales by the Health Protection Agency Centre for Infections. Confirmed cases include those obtained by routine follow-up of all notified cases where IgM is detected in oral fluid.

In 2004, the number of mumps notifications in England and Wales increased to 16 436 from 4204 in 2003. A total of 8104 cases of mumps were confirmed in 2004, compared with a total of 3907 cases in the previous five years. All regions reported more cases in 2004 than in 2003. Cases were predominantly in older teenagers and young adults born before 1987 (figure), and most were in those born between 1983 and 1986. Many of this group are currently at tertiary level education institutions and are associated with outbreaks in universities and colleges across England and Wales. Outbreaks in the same birth cohorts have also been reported in military establishments and prisons.2 Only 2.4% (197/8104) of confirmed cases in 2004 occurred in children who would have been offered two doses routinely—that is, those born between 1993 and 1999 (figure); only 29 of these had documented receipt of two doses of MMR. Only 62 cases (0.8%) have been confirmed in children born after 1999.

Confirmed cases of mumps in 2004 by year of birth (1970-2001) per 100 000 population and opportunity for MMR vaccination (excludes 105 cases of unknown birth year, 351 born in 1914-69, and 30 born after 2001)

• Download figure
• Open in new tab
• Download powerpoint

Comment

During 2004, numbers of notifications and confirmed cases of mumps increased dramatically in all regions across England and Wales, after several years of moderately increased incidence. Most cases are in young adults born before 1988, who would not have been routinely scheduled for MMR during childhood. The highest attack rate was in those born between 1983 and 1986, who were too old to be offered MMR vaccination routinely when it was introduced in 1988, although some may have received one dose of MMR as part of a catch-up programme offered at school entry.3 These individuals would have missed the opportunity for mumps exposure during childhood because high coverage in younger children had reduced circulation of mumps in the UK. Older individuals are more likely to have had mumps when it was still a common childhood infection. The absence of cases in children in younger cohorts, including those affected by the fall in MMR coverage since 1995,4 confirms the effectiveness of the current vaccination policy.

The mumps component of the MMR vaccine used in the UK is believed to offer around 90% protection for one dose, although recent reports indicate that this could be as low as 64%.5 This outbreak confirms that the current, two dose MMR schedule is effective in preventing mumps. In addition to improving routine coverage of MMR, reviewing the vaccination status of all school leavers is recommended, to ensure that they have received two doses of MMR. Other opportunities to offer MMR vaccine to the age group at highest risk, such as when entering university or other institutions, should also be considered.

See also p 1120, and Clinical review p 1132