Vaccine-Preventable Diseases

Mumps

Mumps is an acute infectious disease caused by mumps virus. About 40% of those infected develop acute parotitis, which is unilateral in about 25% of cases. Nonspecific or primarily respiratory symptoms occur in about half of those who acquire infection. Subclinical infection is common. Although complications are relatively frequent, permanent sequelae are rare. Before the widespread use of mumps vaccine, mumps was a major cause of viral meningitis. Mumps meningoencephalitis can, rarely, result in permanent neurologic sequelae, including paralysis, seizures, cranial nerve palsies and hydrocephalus. Transient but occasionally permanent deafness may occur, at an estimated rate of 0.5 to 5.0 per 100,000 reported mumps cases. Orchitis occurs in 20% to 30% of post-pubertal male cases and oophoritis in 5% of post-pubertal female cases. Involvement of the reproductive organs is commonly unilateral; therefore, sterility as a result of mumps is rare. Mumps infection in pregnancy has not been associated with congenital malformations, but mumps infection during the first trimester of pregnancy may increase the rate of spontaneous abortion.

Epidemiology

Since the approval of vaccine in 1969, the number of reported mumps cases has decreased by greater than 99% from an average of 34,000 cases reported per year in the early 1950s to under 400 cases per year in the early 1990s. A further reduction in incidence was observed following the introduction of the routine second dose of MMR. The annual number of reported cases has continued to drop; during the period 2000-2004, an average of 87 cases were reported annually, ranging from 32 (2004) to 205 cases (2002).

In Canada, large outbreaks have been rare in recent years, but three localized outbreaks occurred between 2001 and 2005. The first outbreak, of 193 cases, occurred between September 2001 and March 2002 and involved an under-vaccinated community in northern Alberta following importation of the disease from Bolivia. Most members of the community were philosophically opposed to vaccination. Immunization rates in the affected community were greatly below the provincial average. The majority of cases (80%) occurred in unimmunized individuals, spreading through area schools and to a lesser extent the surrounding community. Two small outbreaks involving 13 and 19 cases occurred in Nova Scotia in the spring and fall of 2005 respectively. The cases ranged in age from 13 to 19 years (average age 14) for the former and 20 to 27 years in a university community (average age 23 years) for the latter. Four of the 13 cases in the first Nova Scotia out-break and all of the cases in the second outbreak reported receiving only one dose of MMR. The latter outbreak resulted in three secondary cases in other provinces.

Globally there has been an ongoing outbreak in the United Kingdom from 2004 to 2006, which has involved > 70,000 cases. Most of the cases have occurred among unvaccinated young adults. The circulating genotype has been identified as genotype G. The G genotype is not an unusual or rare genotype and, like the rest of known genotypes of mumps, it has been circulating globally for decades or longer. In 2005-2006, multi-state out-breaks of mumps involving several hundred individuals, mostly young adults, many of whom had been vaccinated (with one dose of mumps vaccine), have occurred in the United States. These outbreaks have also been identified as associated with genotype G. Mumps remains endemic in many countries throughout the world, and mumps vaccine is used in only 57% of World Health Organization member countries, predominantly in countries with more developed economies.

Source: Canadian Immunization Guide, 7^th edition, 2006

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Links to more information

Guidelines and Recommendations

• For information about Mumps vaccine, see the Canadian Immunization Guide, 7^th edition 2006

Information Sheets

• Childhood Immunization - It's Your Health

Travel Medicine Program

• Mumps