As I write this post, a large outbreak of mumps is ongoing in Columbus, Ohio. The city, which on average sees a single case each year, has seen over 250 since February. To put things in further perspective, only about 440 cases are normally diagnosed in the entire United States annually. The outbreak began on the campus of Ohio State University, where about 150 cases have been identified, but no information about the index case has been reported thus far.

Although the current outbreak will likely smolder for months, the total number of cases thus far is considerably fewer than the worst of the past decade. A 2009-2010 outbreak in New York and New Jersey ended up affecting about 3,000 people. In 2006, about 6,500 college students throughout the Midwest were infected. It is unlikely we will see these kinds of numbers in Ohio, but even our worst in recent years pale in comparison to those that have occurred in England over the past decade, where there was a peak of about 56,000 documented cases in 2005.

The diagnosis of only a few hundred cases per year is a clear victory of the mumps vaccination program, which started in 1967. Prior to the widespread adoption of the vaccine, 186,000 cases were seen in the United States annually. That works out to a decrease in cases of over 99%. This reduction didn’t occur because of improved sanitation, cleaner water, or even sunspots. It occurred because of the hard work and dedication of vaccine researchers, medical professionals and the widespread public acceptance of a safe and effective vaccine.

Mumps doesn’t get the kind of press that measles outbreaks do. There are a number of reasons why this is true and reasonable. I will get into more detail, but essentially mumps, although it can result in significant morbidity, just isn’t as sexy and it isn’t a good candidate for anti-anti-vaccine poster child. Measles wins in that regard, and let’s hope it stays that way. I am terrified at the thought of HiB meningitis returning. But that doesn’t mean that mumps outbreaks can’t serve as fodder for educating the public on vaccines. First though, a primer on mumps.

What is mumps?

Mumps, like measles, is a viral infection for which humans are the only natural host. The single-stranded RNA mumps virus is, also like measles, a member of the Paramyxovirus family of viruses, which is quite an interesting group. This family of viruses also includes respiratory syncitial virus (RSV), which is the major cause of respiratory infection in young children and the most common illness leading to hospitalization in kids under 2 years of age. Croup, another classic pediatric illness, is also caused by a Paramyxovirus, as is canine distemper virus and a morbillivirus that infects dolphins.

Historically, young school-age children were the most likely to be diagnosed, but that changed after vaccination efforts took hold. Over time, an evolution in the epidemiology occurred. After the mumps vaccine was in widespread use, initially the bulk of cases were diagnosed in unimmunized children and adolescents, with 1 out of 10 cases being seen in adults who were born prior to the vaccine becoming available or mandatory for school entry. This led to the current recommendations of a dose of MMR (measles-mumps-rubella) at 12 to 15 months and again at 4 to 6 years of age, as well as documentation of vaccination for college students, although that is only required in 25 states.

As mentioned above, there have been several outbreaks in recent years. Although there have been instances where pockets of children who were not vaccinated have become ill, the majority of cases these days occur in the partially- and even fully-immunized. The most important factor in these outbreaks has been close proximity. Schools, camps and military posts have all been the site of case clusters.

Patients, while still predominantly young, now skew a bit older, in part because of being crammed together in dorms, for instance, but also because of shortcomings in the available vaccine. While the measles component of the MMR is upwards of 99% effective after two doses, the mumps counterpart is only about 80 to 90% effective. So mumps outbreaks, although rendered infrequent and less severe by our vaccine strategy, will likely continue to occur.

Anyone who is susceptible, whether immunized or not and regardless of age, can become ill when exposed to the virus. The mumps virus is very infectious and easily moves from one susceptible person to another, particularly if they are living in close quarters. The virus is spread suspended in respiratory droplets but can also be transferred by direct contact with an infected person or with a virus-carrying fomite. Once infected, the virus usually builds up for a couple of weeks before causing symptoms, but it can be shed in secretions for a few days before the first sign of illness and for several days after.

What does mumps do?

In many people infected with mumps, there are no apparent symptoms. As many as 15 to 20% will be completely asymptomatic in fact. And we think that roughly half of those infected will only have nonspecific respiratory complaints that are indistinguishable from the common cold. Although likely not to the same degree as those with more classic mumps, these lucky individuals still are capable of spreading the infection.

Classic mumps typically also involves some initial nonspecific symptoms, including mild fever, loss of energy and appetite and generalized body aches. What happens next in about 95% of patients is what makes mumps so recognizable to the public. Within a couple of days of the onset of symptoms, both parotid glands (in most cases although not always at the same time) become inflamed, swollen and very tender. This often causes the angle of the jaw to be completely hidden by the swollen tissue and it can last up to 10 days. The one case of mumps I’ve seen, which I diagnosed during a small outbreak in Louisiana in 2010, fit this description.

Although the classic presentation is uncomfortable for patients, it isn’t deadly and there are no long-term problems that result. Unfortunately, mumps is known to cause more serious complications in other areas of the body. Orchitis, inflammation of the testicles, is the most common of these when the patient is a postpubertal male, occurring in about a third of patients. This can result in testicular atrophy and impaired fertility. Sterility is rare but can occur when both testes are involved. A similar phenomenon, oophoritis or inflammation of the ovaries, can occur in postpubertal women although it is much less common.

The most common complication of mumps after involvement of the parotid glands, however, is meningitis. Luckily, it is often mild, perhaps only causing headache, but it can be more significant in 4-6% of cases. The prognosis is excellent with full neurologic recovery expected. Mumps can also cause encephalitis, which is widespread inflammation of the brain itself rather than just the outer covering as with meningitis. Before the vaccine, mumps encephalitis was the most common viral cause of the condition, occurring in about 1 out of every 6,000 cases. Mumps encephalitis causes fever and changes in mental status (by definition), and can result in seizures, weakness and even transient paralysis. Like viral meningitis, recovery tends to be complete.

Prior to the mumps vaccine, many children suffered hearing loss because of the infection. It typically only involved one ear, and the degree of hearing loss was variable. But cases of permanent bilateral deafness were known to happen.

There are more associated complications, such as Guillain-Barre syndrome and facial palsy. There have also been reports of arthritis, pancreatitis and even fatal inflammation of the heart, but these are considered to be rare. One very good bit of news is that mumps, as opposed to rubella (also included in the MMR vaccine) is not associated with birth defects when a pregnant woman is infected. Congenital rubella is an awful syndrome, much worse than mumps and even measles, and has become extremely rare because of the vaccine.

What do we do about mumps?

There is no specific treatment for mumps. The general approach is to reduce symptoms with medicines for fever, if the patient is uncomfortable, pain and inflammation. Often this can be accomplished with the same medicine, ibuprofen being a good choice. Some patients find the use of warm and/or cold packs helpful in dealing with a tender and swollen parotid gland. Ice, and elevation of the swollen scrotum, along with ibuprofen, can ease symptoms of patients with orchitis.

Hospitalization is rarely necessary, but may be warranted in cases of meningitis, encephalitis, or pancreatitis. The case I admitted back in 2010 was initially misdiagnosed in the emergency department as having a bacterial infection of the parotid gland, something which would be extremely rare in a child. But then again, so is mumps. And we weren’t aware of the small cluster of cases at the time.

The most important aspect of managing mumps is preventing spread to others. Isolation is often recommended for up to 5 days after onset of symptoms. Vaccination of susceptible individuals exposed to a patient with mumps is also recommended, although to date there are no studies supporting its efficacy in preventing symptoms from that exposure. The goal of this CDC recommendation is primarily to prevent infection from a new exposure during a current outbreak or from one in the future.

What the CDC Advisory Committee on Immunization Practices (ACIP) considers to be an adequate immunization status changed after the 2006 outbreak. Instead of one dose of MMR for children in kindergarten through 12th grade being considered adequate, they now require two. This is also true for high-risk adults, which includes those who work in healthcare facilities, travelers to mumps-endemic regions and college students. During an outbreak, they recommend giving a 2nd dose early to children aged 1 to 4 years and all adults. There is some evidence from the 2009 outbreak to support that offering a third dose might be helpful in decreasing spread of the infection, although this has yet to be replicated.

So why all the mumps?

The vaccine for mumps is a component of the MMR (technically also the MMRV, which includes varicella), the same MMR that has been the focus of controversy manufactured by a vocal minority of anti-vaccine celebrities, politicians and pseudoskeptical researchers over the past several years. The anti-vaccine movement, particularly in the UK, is clearly linked to an increase in vaccine-preventable illnesses and many experts are worried that we haven’t seen the worst yet. This has been covered extensively on Science-Based Medicine in the past.

The mumps component of the MMR, just like the measles vaccine, contains a weakened but live virus that has been processed using animal cells. Since 1978, the Jeryl Lynn vaccine strains have been used to make all mumps vaccine in the United States. This combination of two strains was cultured from the throat of Jeryl Lynn Hilleman, daughter of mumps vaccine developer Maurice Hilleman, in 1963. Hilleman developed eight of the current vaccines in use and is credited as saving more lives than any other scientist in the 20th century, although Norman Borlaug fans may not agree.

Where the similarity between the mumps and measles vaccines ends is when we look at effectiveness. We know that the mumps vaccine works pretty well. There is simply no other explanation for the dramatic decreases in incidence after it came on the scene. But continued sporadic and sometimes significant outbreaks speak to the fact that we certainly wish it worked better. The measles vaccine, after two doses, results in roughly 99% of people being protected from disease if exposed. With mumps, even with two doses, that drops to somewhere around 85%, with a range of 60-90%. That difference is especially meaningful considering that even if there was 100% uptake of the vaccine, herd immunity for mumps kicks in when about 92% of the population is immune.

When studies have compared the percentage of individuals becoming infected after exposure in unvaccinated and vaccinated populations during actual outbreaks, the effectiveness of the vaccine hasn’t matched the results of clinical trials. Not that the benefit isn’t significant though. With two doses of MMR, only 2 to 4% were infected while a little more than a third of those having received zero doses became ill. It’s a good vaccine, but 4% of thousands can add up. And because most people are vaccinated, at least in the United States, so are most people infected with mumps.

Some outbreaks, the one is 2006 that involved the United States, Canada and the UK being the prime example, involved a serotype that differed from the one used in the MMR vaccine. Differences were found in immune response in vitro, although vaccine-induced antibodies obtained even from serum 11 years after vaccination still appeared to work against the outbreak strain. But researchers remain uncertain about differences of effectiveness in natural infections. Half the amount of neutralizing antibodies may be enough in vitro but not in the real world. The question of waning immunity has been raised as well. So far the evidence is mixed, and there does not appear to be much talk of adding a third dose during adolescence or early adulthood.


At one point, there was a goal of eradicating mumps in the United States by 2010. Sadly, this didn’t happen and probably can’t be accomplished given the less-than-ideal effectiveness of the vaccine currently available and the ease of bringing mumps back into the country after visiting areas with higher prevalence. Recent mumps outbreaks, unlike those involving measles infections, are not a result of vaccine refusal, although that certainly may change if the number of vaccinated people were to continue to decrease.

Mumps isn’t the worst of the vaccine-preventable illnesses by a wide margin. But it can cause significant morbidity, including deafness and impaired fertility, and the symptoms of classic mumps can be extremely uncomfortable even if they won’t kill you. The MMR vaccine is extremely safe and is pretty good at decreasing your risk of becoming infected if exposed. It’s even better at protecting you from measles and rubella. So there is just no excuse unless you have a true medical contraindication. And even if you become infected after vaccination, your illness may be less severe than it might have been otherwise.


Posted by Clay Jones

Clay Jones, M.D. is a pediatrician and a regular contributor to the Science-Based Medicine blog. He primarily cares for healthy newborns and hospitalized children, and devotes his full time to educating pediatric residents and medical students. Dr. Jones first became aware of and interested in the incursion of pseudoscience into his chosen profession while completing his pediatric residency at Vanderbilt Children’s Hospital a decade ago. He has since focused his efforts on teaching the application of critical thinking and scientific skepticism to the practice of pediatric medicine. Dr. Jones has no conflicts of interest to disclose and no ties to the pharmaceutical industry. He can be found on Twitter as @SBMPediatrics and is the co-host of The Prism Podcast with fellow SBM contributor Grant Ritchey. The comments expressed by Dr. Jones are his own and do not represent the views or opinions of Newton-Wellesley Hospital or its administration.