Disease Risk – Mumps

 

Risk to a child from Mumps if not vaccinated until after the age of 5:

Case Fatality Rate: The WHO reports the case fatality rate worldwide at 1 in 10,000 cases.[1]  In the USA, an average of one death per year occurred from 1980-1999.[2]

Rate of Long Term Sequelae or Injury: Mumps can cause encephalitis (2 per 100,000 cases) and deafness (5 in 100,000 cases)[1][2][3]. In 80% of the deafness cases, the hearing loss is reported to be unilateral (affecting one ear).[2]  Infection in older males can also result in sterility, but this is not a risk to the under five population.

Incidence Rate: From 2004 – 2008 the average number of mumps cases per year was 1682 with typical years resulting in around 500 cases and periodic larger outbreaks (6,500 cases in 2006).[4]

Incremental Risk in highly vaccinated population (if a child does not vaccinate by age 5):

In the mumps outbreak in the USA in 2006 [5], mumps outbreaks occurred primarily on college campus in the Midwest.  A total of 6584 cases and 85 hospitalizations were reported in 2006; no deaths occurred.  No large outbreaks were reported at primary or secondary schools. In the 18-24 years age group, the incidence of mumps was higher than in all the other age groups combined by a factor of 3.7. Of the patients with known vaccination status, less than 4% of those under the age of 30 years were unvaccinated. Only about 3.3% of the cases occurred in children under age 5, with an incidence rate of approximately 40/10,000 for age <1 and 180/10,000 for ages 1-4. Neither vaccination status nor race or ethnic group was significantly associated with complications.

Approximately 3.5% of cases occurred in the under five population in the USA 2006 mumps outbreak [5]. Based on the average number of cases from 2004 – 2008 (1682), the average number of cases in children under five would be 59.  The WHO reports the case fatality rate worldwide at 1 in 10,000 cases [1].  Assuming that the risk of death is only to unvaccinated children, and assuming a max vaccination rate of 96% [5], then the cumulative risk of death to the child over the first five years of life was calculated to be 0.00036 per 10,000 children or a 1 in 27,911,286 risk.

Encephalitis occurs at a rate of 2 in 100,000 cases and deafness results in 5 in 100,000 cases [3].  Assuming that the risk of encephalitis or deafness is only to unvaccinated children, and assuming a max vaccination rate of 96% [5], then the cumulative risk of permanent injury to the child over the first five years of life was calculated to be 0.00025 per 10,000 children or a 1 in 39,873,265 risk.

Incremental Risk in population with low vaccination (if a child does not vaccinate by age 5):

Assuming that infection levels increased to USA pre-vaccine levels in 1964, when there were approximately 212,000 cases per year [3] in a population of 192,000,000 [7], then the incidence rate would be 11 per 10,000 each year.

The WHO reports the case fatality rate worldwide at 1 in 10,000 cases [1].  The cumulative risk of death to the child over the first five years of life was calculated to be 0.00552 per 10,000 children or a 1 in 9,056,604 risk.

Encephalitis occurs at a rate of 2 in 100,000 cases and deafness results in 5 in 100,000 cases [3].  The cumulative risk of permanent injury to the child over the first five years of life was calculated to be 0.00386 per 10,000 children or a 1 in 12,938,006 risk.

 

 

References:

[1] http://www.who.int/immunization_monitoring/diseases/mumps_surveillance/en/index.html

[2] Mumps in Emergency Medicine. http://emedicine.medscape.com/article/784603-overview#a0199

[3] Centers for Disease Control and Prevention: Epidemiology and Prevention of Vaccine-Preventable Disease. Atkinson W, Wolfe S, Hamborsky J, McIntyre L. eds. 11th edition. Washington D.C.: Public Health Foundation, 2009.

[4] Center for Disease Control and Prevention.  Notifiable Diseases/Deaths in Selected Cities Weekly Information.  MMWR2009; 58(45): 1276-1287.

[5] Recent Resurgence of Mumps in the United States.  N Engl J Med 2008; 358:1580-1589, April 10, 2008.  http://www.nejm.org/doi/full/10.1056/NEJMoa0706589

[6] CDC.  MMWR on Mumps.  MMWR 32(42): 545.

[7] http://www.census.gov/popest/archives/1990s/popclockest.txt