By Amesh A. Adalja, MD, FACP, FACEP, March 7, 2014
Several vaccine-preventable diseases are reappearing, seemingly as a result of waning immunity, lax attitudes about vaccination, and importations from abroad. Pertussis and measles are 2 that occur with some regularity, but mumps outbreaks have occurred as well. The recent announcement of a 13-person cluster of mumps cases among a highly-vaccinated student body at Fordham University underscores the fact that immunity can wane over time.1
Mumps is a viral illness characterized by swelling of the salivary glands, a featured noted by Hippocrates in the 5th century BC. Most cases are uncomplicated; however, in rare instances, meningoencephalitis may occur. Epididymo-orchitis can occur in up to 25% of males, especially those who are post-pubertal. After an incubation period of 16-18 days, nonspecific viral symptoms may occur, followed by parotid gland tenderness and swelling within 1 day. Up to 20% of cases are asymptomatic.2,3
Vaccination against mumps has been available since 1967 in the US. Current recommendations call for 2 doses, with the first administered at age 12-15 months and the second at age 4-6 years as part of the combined MMR or MMRV vaccines. A 2-dose regimen confers immunity to 88% of those vaccinated, and coverage rates are very high within the US.3
Before the Fordham outbreak, 2 other recent outbreaks of mumps caused large blips in the number of US cases. The first occurred in 2006 when an outbreak centered on an Iowa college campus eventually accrued 6,584 cases. The majority of patients were adequately vaccinated. The other outbreak occurred in the northeast US in 2009, and was sparked by a boy who had travelled to the UK in the midst of an outbreak there. Again, most of the patients were appropriately vaccinated.3
It is not clear why mumps outbreaks are occurring highly vaccinated populations. What makes these outbreaks particularly puzzling is that the 2-dose vaccine regimen provides robust immunity and has seemingly controlled mumps in the past. Further, a third dose did not demonstrate a statistically significant protective effect when administered during the 2009 outbreak.4 Past and current experiences, therefore, raise important questions that warrant study:
How are the outbreak strains related to the vaccine strains?
Why are mumps outbreaks occurring now instead of when vaccine coverage was lower?
Does crowding in college dormitories overwhelm immunity?
Are there super-spreaders whose viral shedding exceeds vaccine protection?
Thirteen Fordham students believed to have mumps. CBS New York. http://newyork.cbslocal.com/2014/02/20/13-fordham-university-students-believed-to-have-mumps. Accessed March 4, 2014.
Litman N, Baum SG. Mumps virus. In: Mandell GL, Bennett JE, Dolin R, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, PA: Churchill Livingstone; 2010.
Mumps. CDC Web site. http://www.cdc.gov/mumps. Accessed March 4, 2014.
Parker Fiebelkorn A, Lawler J, Curns AT, et al. Mumps Postexposure Prophylaxis with a Third Dose of Measles-Mumps-Rubella Vaccine, Orange County, New York, USA. Emerg Infect Dis. 2013. Sep;19(9): 1411-7. http://wwwnc.cdc.gov/eid/article/19/9/13-0299_article.htm. Accessed March 4, 2014.
Clinicians' Biosecurity Resource