At the Montgomery County Pediatric Society meeting on December 4, 2017, Dr. Stuart Taylor asked me a very thought-provoking question. During a discussion of the numerous mumps outbreaks on college campuses and elsewhere recently, he wondered whether the effort and expense of tracking cases and immunizing in special situations was worthwhile, considering that mumps is a relatively mild illness. He recalled being told some decades ago that the mumps vaccine was included with the measles and rubella vaccines, both of which protect against infections with very serious complications, more out of convenience than for a compelling public health benefit. That question sent me back to the medical literature, and I learned (or maybe re-learned) some interesting points. Bottom line: mumps isn't as mild as most pediatricians think.
I wanted to first find recent information on mumps in more industrialized countries, but that isn't as easy as it sounds. However, studies on mumps outbreaks primarily in adolescents in England in 2004-5 offer some sobering statistics. In the United Kingdom, MMR vaccine was introduced in 1988 as a single dose for children 12-15 months of age, followed by a recommendation in 1996 to add a second dose to the routine immunization schedule. The 2004-5 epidemic largely affected individuals who were born too early to be offered the initial vaccine, but also protected somewhat during their childhood by a high vaccination rate in younger children, such that they weren't as likely to be exposed to the wild virus. Yung et al mined various databases in England and Wales from 2002-2006 and estimated that mumps infection resulted in 2647 case-patients being hospitalized, or about 6% of all mumps cases. That alone certainly would justify universal mumps immunization programs. These investigators also estimated hospitalization rates for some of the mumps complications: 4.4% for orchitis, 0.35% for meningitis (note aseptic meningitis is very common in mumps, about 50%, but is very mild usually), and 0.33% for mumps pancreatitis.
Mumps also is a cause of hearing loss, sometimes severe. A recent Japanese study was able to locate and confirm 67 cases of mumps hearing loss. Only 15 of them had obvious clinical mumps infection by history, and over 90% of these cases had severe hearing loss, though this latter figure may be inflated due to ascertainment bias. It is important to note that Japan is an outlier among developed countries in how they immunize for measles, mumps, and rubella.
A few interesting references:
Hviid A, et al. Mumps. Lancet 2008; 371:932-44.
IASR. Mumps (infectious parotitis) in Japan, as of September 2016. IASR 2016; 37:185-6. Online at https://www.niid.go.jp/niid/en/index-e/865-iasr/6843-440te.html.
Morita S, et al. The clinical features and prognosis of mumps-associated hearing loss: a retrospective, multi-institutional investigation in Japan. Acta Oto-laryngol 2017; 137 (Suppl 565):S44-7.
Yung C, Ramsay M. Estimating true hospital morbidity of complications associated with mumps outbreak, England, 2004/5. Euro Surveill 2016; 21, online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4998425/.
Yung C-F, et al. Mumps complications and effects of mumps vaccination, England and Wales, 2002-2006. Emerg Infect Dis 2011; 17:661-7.