College Mumps Cases Here, There and Everywhere
Mar 18, 2016

As a parent of a college student it concerns me to hear of so many reported mumps cases on various college campuses throughout the nation. 

In just the past week, I’ve read about cases at the following colleges:   University of San Diego (5), Harvard University (13), Boston University (3), Tufts University, The University of Massachusetts Boston, Bentley University, University of Southern Maine, Indiana University (12), Butler University (21), IUPUI (3), SUNY Buffalo, University of Kentucky and University of Louisville.  Now there are even reports of new cases in elementary, middle and high schools in Montana and cases expanding in Monroe County just outside of Indiana University.

While there are far fewer cases of mumps these days (1,057 cases in 2015) compared to the years before the vaccine was introduced, I can’t help but wonder what is prompting these recent outbreaks.

Mumps is typically so uncommon that just a few cases in one geographical area can constitute an outbreak.  However, these recent outbreaks seem to be occurring mostly on college campuses, but they are not isolated to one geographic region.

Are we to suspect that the behavior and living conditions among college students is contributing to the transmission of mumps among this particular age group more so than among other age groups?

After all, mumps is a contagious disease that is spread through coughing, sneezing, close contact and saliva exposure with infected people.  One such explanation offered in The Journal of Infectious Diseases suggests that

“High population density in communal living situations, such as dormitories and boarding schools, may provide increased opportunities for close contact or saliva exposures and higher dose exposures to mumps virus when introduced, resulting in easier transmission and higher rates of disease than might occur in other parts of society”.

This seems plausible, but there are likely other factors at play as well.

Could these outbreaks be the result of lower vaccine efficacy, waning immunity or a reduced herd immunity threshold?

It’s common for outbreaks to occur when a disease is introduced into a community from an outside source, such as someone who returns to, or visits, the U.S. after having been infected while traveling or living abroad.  However, this does not appear to be the case in these most recent outbreaks, and so we are left wondering if we could be seeing the early signs of waning immunity.

The current recommendation for the MMR vaccine (which is intended to prevent measles, mumps and rubella) is an initial dose between 12-15 months of age and another between 4 and 6 years of age.  According to the CDC, mumps vaccine is believed to be about 88% effective in individuals who’ve had the recommended two doses, and about 78% effective in those who received just one dose.  While mumps vaccine is not as effective as some other types of vaccines, such as measles which happens to be about 97% effective, the vaccine has been effective in keeping cases to a minimum, with the exception of a few outbreaks.

For example, in 2006, a multi-state mumps outbreak resulted in more than 6,500 reported cases. This resurgence predominantly affected college-aged students living in the Midwest, with outbreaks occurring on many different Midwestern college campuses.  During 2009-2010, two large outbreaks occurred. One was among a close-knit religious community in New York City with 3,502 reported cases which began when an infected student returned from the U.K. where a large mumps outbreak was occurring.  The other outbreak involved about 505 people on the U.S. Territory of Guam. More recently, in 2011-2013, there were several smaller mumps outbreaks on college campuses in California, Virginia and Maryland.  However, these had very limited spread and didn’t seem to result in high case counts for those years.

Perhaps this is what we are seeing now; small isolated mumps cases with limited spread.  But in looking more closely at the number of cases per year, we may also be at the beginning of an upward trend with 1,223 in 2014, and 1,057 in 2015.  As of March 4, 2016 the CDC has reported about 250 cases.  But with all these college outbreaks so early in the year, how high will the numbers go by the end of 2016? 

There is another concern related to these college cases.  Some of the news reports have noted that these outbreaks involve vaccinated individuals. 

This is not to say that unvaccinated individuals are not getting mumps, because they can, and they are.  This also doesn’t suggest that vaccinated individuals are more likely to get mumps, because they aren’t. It’s just a simple matter of numbers. There are just more vaccinated individuals than unvaccinated individuals, so it mathematically more probable that when outbreaks occur they hit those with low or no immunity.  This includes all the unvaccinated individuals, as well as a small percentage of vaccinated individuals.  The questions that are raised pertain more to waning immunity among those vaccinated and the herd immunity threshold.

 Waning immunity is likely, as explained in the article Mumps Control Today,

“Over time, immunity may wane, even after receipt of 2 doses. This perhaps provides a reason for today’s outbreaks occurring primarily among young adults. This has resulted in suggestions that a third dose may be needed or that the second dose of MMR vaccine should be given during adolescence rather than just before school entry at 4 or 5 years of age. One study showed that the 2-dose vaccine efficacy decreased from 99% among 5–6 year-olds to 86% among 11–12 year olds.”

Even though mumps vaccine isn’t 100% effective, it remains the best way to prevent an infection. We know that the second dose of MMR (the measles, mumps and rubella vaccine) is recommended to produce immunity in those who did not respond to the first dose.  Unfortunately, studies also show that a very small percentage of people may not be protected even after a second dose.  Since we know that some vaccinated individuals will not confer immunity, and some conferred immunity will wane over time, we must recognize that a portion of the vaccinated population may not have adequate immunity to mumps by the time they are young adults.  If we factor in the people who were never vaccinated, either because they had medical contraindications, or because they simply refused the vaccine, we see that there is a percentage of the population that remains at risk to disease.  If that percentage drops below the herd immunity threshold, which for mumps is suggested to be between 88%-92% than we can expect outbreaks.  Therefore, we need to examine if this is what is happening, or if the herd immunity threshold actually needs to be higher than previously suggested?  

Another consideration is that these outbreaks are, in part, an unfortunate result of the vaccine’s success.

We know that successful immunization programs work to reduce the wild strain of the disease, but we also know that natural exposure can help to boost immunity among the general population.  Here are two explanations offered in The Journal of Infectious Diseases.

Over time, “the vaccine strain (derived from genotype A) may be less effective against serogroup G wild strains (the type seen in the United States)”

Additionally, “vaccine efficacy and corresponding antibody levels may be lower than expected, especially now that natural boosting due to disease exposure is very rare (estimates of the effectiveness of the mumps vaccine have varied but have been estimated to be as low as 64% after 1 dose and 79% percent after 2 doses.”

A review of available literature shows that these mumps outbreaks have been receiving a fair amount of attention recently.  If we continue to see additional outbreaks, I believe we will be hearing more about the need to investigate all possible causes and potential solutions.

While mumps is usually a mild disease, the virus does cause salivary glands to become swollen and tender on one or both sides of the face. Other symptoms include fever, headache, muscle aches, tiredness and loss of appetite that can last up to 10 days.  In addition, about one out of every four teenage or adult men who get mumps will develop a painful swelling of the testicles, and in rare cases this can lead to sterility.  Mumps can also cause rare complications such as meningitis (swelling of the brain and spinal cord) and deafness.  While it is expected that most people in the U.S. will recover well, there is still reason to expect the vaccine to prevent large numbers of cases and outbreaks from occurring.

Right now, the best way to prevent mumps is to vaccinate yourself and your family and encourage others to do the same.  You may also want to advise your college student not to swap spit with anyone or they run the risk of suffering an uncomfortable illness and a likely quarantine.  It’s unlikely this parental advice will be well received, but it couldn’t hurt.   

 

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