Oh man, mumps!
Washington State is in the midst of a mumps outbreak. We weren’t the first (Arkansas has about 2500 cases), but we’re giving it our best effort! So far there are 300 cases. Why is this happening? Why should we care? Why bother getting the vaccine if the disease can happen anyway?
What is mumps?
Mumps is a virus spread by respiratory droplets that is famous for causing inflammation of the salivary glands below the ear (parotitis) but can also cause inflammation of the testes (orchitis), ovaries (oophoritis) and breasts (mastitis), as well as deafness and inflammation of the lining of the brain and spinal cord and the brain itself (meningitis, encephalitis). Rarely it can cause death.
Mumps virus can be found in the saliva and respiratory droplets from 7 days before to 9 days after onset of salivary gland swelling, but fewer than 15% of patients continue to shed virus beyond 4 days, and so typical precautions are to isolate the patient until 5 days after onset of symptoms. Not everyone experiences salivary gland swelling. Because it’s contagious for days before symptoms appear, it’s obvious that it would be easy to spread, without even knowing you’re sick.
We currently vaccinate for mumps as part of MMR (measles-mumps-rubella, brand name M-M-R II by Merck). The mumps vaccine was licensed in 1967 and then included in the MMR vaccine that was licensed in 1971. While the rubella component of that vaccine changed in 1979, the measles and mumps components have remained the same since then. Our mumps vaccine uses the Jeryl-Lynn strain (named after the developer’s daughter – he isolated the virus from her while she was sick with mumps). There are other strains of mumps virus also in use – the Rubini strain in Switzerland primarily, and the Urabe strain in Japan and some European countries. The Leningrad-3 strain was used in the former Soviet Union and Slovenia, and the L-Zagreb strain (a further weakened version of the Leningrad-3 strain) was used in Croatia and Slovenia. When we study how well a mumps vaccine is working, it’s important to remember that different forms of the mumps vaccine may use different strains, and it seems that some work better than others. A study showing an outbreak in a vaccinated population using a different strain than is used in your community may not be applicable commentary on how protective your vaccine would be.
Our schedule has also changed – from 1963 to 1989, there was one dose given in infancy (originally at 9 months, then at 12-15 months), and now the firs dose is given at 12-15 months and a second dose at 4-6 years. That second dose was added in 1989 after a significant measles outbreak, when it was noted that some small portion of the vaccinated children failed to respond to the vaccine.
Side note: this measles outbreak was also when it became clear that many children were not being vaccinated because of access issues, and this is when the Vaccines for Children program1 was started, to improve access to vaccines, and try to reduce the financial and logistical challenges standing between children and immunity. It’s estimated that the VFC program has already saved 732,000 lives, prevented 322 million illnesses, and saved $1.4 trillion in total societal costs.
Between 1989-1999 there was also a catch-up dose recommended for children 10-11 years old to try to get as many kids protected as possible, since those kids wouldn’t be covered by the recommendation for a kindergarten dose. It’s possible to have received one dose on schedule and never have gotten the second dose, depending on the timing, how attentive your doctor was to the catch up dose recommendation, how often you went to the doctor, etc. Do you know if you’ve gotten one or two doses of MMR?
How many cases of mumps were there in the pre-vaccine era?
Before 1967, when immunization for mumps started, mumps was a universal disease. That means everyone got it.
Mumps was first described by Hippocrates 2, who described in young men swelling around one or both ears, often accompanied by painful swelling of one or both testicles. During World War I, it was the leading cause of days lost from active duty in US troops deployed in France, and was the number three cause of hospitalization (only behind influenza and gonorrhea). Over the 1900s, it was identified as being caused by a virus, and by the 1950s, a vaccine had been developed in the Soviet Union, and by the 1960s, a vaccine had been developed in the United States.
With the introduction of the vaccine, cases were reduced 99%.
If you can still get the disease, why bother getting vaccinated?
In King County, about 92% of children entering kindergarten in public school have received 2 doses of MMR. The article in Outbreak News Today4 describes about 63% of the cases were vaccinated. If the vaccine were not effective at all, you would see the same rate of vaccination in the has-the-disease population vs the doesn’t-have-the-disease population, but it’s significantly lower. The vaccine reduces the risk of getting the disease, with efficacy estimated at 88% 5.
The vaccine reduces the risk of getting the disease, but the vaccine also reduces the risks associated with getting the disease.
It isn’t just whether or not you get a disease, but how serious the disease ends up being in your (or your child’s) body. Will you have a mild version? Or will you have severe effects, with permanent injury?
With every case of mumps, you’re rolling the dice. The more mumps, the more instances of complications.
For example, temporary deafness occurred in 4% of infected people in one studied population. If there are 100 cases, we’d expect to see 4 cases of temporary deafness. But if there are 1000 cases, that’s 40 cases of temporary deafness. The more cases, the more instances of complication. Permanent deafness occurs in 1 in 20,000 infected people. Before the vaccine, mumps was a leading cause of deafness in children. That’s why it’s so important to keep the overall number of cases low. The fewer times you roll the dice, the less likely it is that your number will come up.
It’s clear comparing rates between the pre-vaccine era and post-vaccine era that the vaccine reduces the number of cases, and in doing so, the number of complications. Most studies also show that someone being vaccinated reduces the risk of them developing a complication even if they do get the disease. This is called reducing disease severity and it was studied in outbreaks among Orthodox Jewish boys in New York and surroundings6 where receipt of the recommended two doses reduced the risk of orchitis (and limited the spread of the disease outside of the immediate community). Even more reduction of disease severity was seen in a community in the Netherlands7 where receipt of the recommended two doses of vaccine reduced the risk of overall complications, orchitis and hospitalization.
Even mild mumps is uncomfortable. The fever, swelling, jaw pain, testicle pain – even if it doesn’t result in sterility or deafness, is it really how you want to spend your week? Is it really an experience you want your child to have?
Why do we still get outbreaks?
This is a great question, and the answer is multifactorial.
It’s likely that immunity from the vaccine wears off some over time.
In the presence of an outbreak, especially with intense exposure, the viral dose may overcome that immunity. That’s one of the theories associated with the outbreak in the Orthodox Jewish community. In that community, boys study in an intensive style, in pairs, in animated discussion, face to face, for up to 15 hours a day. They would have received a higher dose of respiratory droplets than people who are just in casual contact. The dynamics associated with that outbreak – most cases among the boys, then less in their household as they brought it home, and hardly any cases in the surrounding communities – supports that theory.
Is the virus ‘mutating’ in response to the vaccine? A study in Switzerland3 analyzed the viral strains found in complicated mumps cases and did not find any evidence to support the idea of “vaccine escape mutants.”
Don’t stay mum on mumps vaccine!
The vaccine significantly reduces the risk of getting the disease, and it reduces the risks of getting the disease. Complications are rare among the vaccinated, but can be serious among the unvaccinated. Adults aren’t exempt here – make sure your kids are up to date, and make sure you are too.
- VFC | About the Program | Vaccines for Children Program | CDC [Internet]. [cited 2017 Jan 27];Available from: https://www.cdc.gov/vaccines/programs/vfc/about/
- Plotkin S, Rubin S. Mumps vaccine. In: Vaccines. Saunders; 2012.
- Utz S, Richard J-L, Capaul S, Matter HC, Hrisoho MG, Mühlemann K. Phylogenetic analysis of clinical mumps virus isolates from vaccinated and non-vaccinated patients with mumps during an outbreak, Switzerland 1998-2000. J Med Virol 2004;73(1):91–6.
- Washington mumps outbreak nears 300 cases [Internet]. Outbreak News Today. 2017 [cited 2017 Jan 27];Available from: http://outbreaknewstoday.com/washington-mumps-outbreak-nears-300-cases-88245/
- Livingston KA, Rosen JB, Zucker JR, Zimmerman CM. Mumps vaccine effectiveness and risk factors for disease in households during an outbreak in New York City. Vaccine 2014;32(3):369–74.
- Barskey AE, Schulte C, Rosen JB, et al. Mumps Outbreak in Orthodox Jewish Communities in the United States. N Engl J Med 2012;367(18):1704–13.
- Sane J, Gouma S, Koopmans M, et al. Epidemic of Mumps among Vaccinated Persons, the Netherlands, 2009–2012. Emerg Infect Dis 2014;20(4):643–8.