In case you missed it, there’s a mumps outbreak in the NHL that’s causing quite the stir.
HealthMap’s Disease Daily explains how these kinds of outbreaks can happen — even if most people are vaccinated.
This post originally appeared on HealthMap’s Disease Daily on May 8, 2014. It has been reposted here with permission from the authors.
By Jane Huston and Robyn Correll Carlyle
When we hear the word mumps, we picture a young boy wearing wool trousers and suspenders with comically swollen cheeks, left behind while his family takes the brand new Model T to town to see the latest Charlie Chaplin flick. Maybe we’re too imaginative but nonetheless, it sounds like a disease from the past.
So, imagine our surprise when we started hearing reports of a mumps outbreak at Ohio State University (OSU) in early January. What started as a few cases has now spread to more than 300 people throughout the state. And news of other mumps outbreaks have cropped up at Fordham University in New York and the University of Illinois.
The kicker? Most of those affected have been vaccinated.
How is this possible? If these people were vaccinated, how did they still get mumps? Wasn’t the vaccine effective?
The answer is complicated, and there are a few things you need to consider:
1. The majority of people getting sick with the mumps are vaccinated — but that’s because almost everyone is. The percent of small children in the United States with at least one dose of the MMR vaccine has been at or above 90 percent for nearly two decades now.
2. No vaccine is 100 percent effective. But then again, no surgical procedure or medication is either. Even Google goes down occasionally.
The mumps component of the MMR (measles, mumps, rubella) vaccine is between 75- 91 percent effective, and effectiveness is higher with two doses. As a result, up to 10-15 percent of those who get a mumps vaccine won’t actually develop sufficient antibodies to provide immunity, especially during an outbreak.
This can be for a few different reasons: First, the MMR is a live vaccine, which means that it needs to be kept alive to work. If a vaccine is not stored or handled properly, that vaccine can lose its potency and become less effective at helping your body produce antibodies. This is a particularly large challenge in developing countries, where the electricity and infrastructure needed to keep the vaccine at optimal temperatures is sometimes infrequently available. But power outages can happen in the United States, too, and if vaccines aren’t handled properly en route from the manufacturer to the provider’s office or pharmacy, there’s a chance they won’t be as effective.
Second, as much as we want to believe there can be a one-size-fits-all approach in medicine, human bodies aren’t all the same, and not all immune systems will react in the exact same way to vaccines. As a result, there are individuals who, for one reason or another, do not develop an immune response after vaccination, or who do develop some protection against a disease, but that protection is incomplete or temporary.
Fortunately, even if a vaccine fails in an individual, that person has something to fall back on: herd immunity. We’ve written about herd immunity before, and explained its role in protecting those who can’t get vaccinated for age or medical reasons. But herd immunity also protects those who are vaccinated and (unknowingly) do not generate the appropriate immune response.
3. Protection from a disease is not an all-or-nothing thing. Here’s an example: Say you are someone who got one dose of the vaccine and developed a weak, but present, immune response. Those antibodies will probably protect you if you come into contact with one infected individual in passing, but multiple infected individuals in close quarters? Probably not. Your immune system can handle a small amount of exposure to mumps, but not a full-on assault, which is what happens when you get those infected with the mumps in close proximity with a lot of other people — in a college dormitory, for example, or a crowded lecture hall.
4. Even with “breakthrough” cases, vaccination is still our best defense against the mumps. Before vaccination campaigns began in 1967, there were about 186,000 cases every year. In 2013, there were 438. Vaccination has resulted in a roughly 99 percent decrease in the number of mumps cases. So think of how much worse these outbreaks would be if vaccination rates weren’t already high.
Even if you do get the disease after getting vaccinated, chances are it will be a much milder illness. And while mumps might look like nothing more than a case of chipmunk cheeks, it can cause some pretty severe complications like pancreatitis or deafness. Prior to routine vaccination against mumps, 15 percent of cases suffered meningitis, two to five percent pancreatitis, and on rare occasions (about 1 in 20,000), patients could go deaf as a result of mumps infection.
Of the 309 cases of mumps in Ohio so far, there have been only three hospitalizations. If we applied pre-vaccination era hospitalization rates to the same number of cases, that number would be roughly five times higher.
So if anything, these mumps outbreaks demonstrate why vaccines are so important, and why everyone who can be immunized should be.
Unless, of course, you’re into chipmunk cheeks.
Jane manages the Vaccine Finder project at Health Map, the host site of the Disease Daily. Robyn is a contributing writer for the Disease Daily and works as a project manager for a non-profit focused on vaccine education. Both are fully up-to-date on their immunizations.