# Why the mumps outbreaks? **URL:** \ **Category:** Factual Questions\ **Created:** [December 6, 2016, 2:19pm UTC](https://boards.straightdope.com/t/why-the-mumps-outbreaks/774016 "2016-12-06T14:19:52Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Urbanredneck](https://avatars.discourse-cdn.com/v4/letter/u/ea5d25/32.png) [@Urbanredneck](https://boards.straightdope.com/u/Urbanredneck)\ **Post date:** [December 6, 2016, 2:19pm UTC](https://boards.straightdope.com/t/why-the-mumps-outbreaks/774016/1 "2016-12-06T14:19:52Z")
It has been[reported](https://www.insidehighered.com/quicktakes/2016/12/05/mumps-outbreaks-hit-colleges)that on many college campuses they are seeing outbreaks of the mumps. Thing is almost all those with mumps received required vaccinations. I dont get it. Isnt a vaccine supposed to protect one from a disease? ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [December 6, 2016, 2:26pm UTC](https://boards.straightdope.com/t/why-the-mumps-outbreaks/774016/2 "2016-12-06T14:26:44Z")
[From the CDC](https://www.cdc.gov/mumps/outbreaks.html) > [@](#): > > MMR vaccine prevents most, but not all, cases of mumps and complications caused by the disease. Two doses of the vaccine are 88% (range: 66 to 95%) effective at protecting against mumps; one dose is 78% (range: 49% to 92%) effective You’ll also note that the outbreak is currently inline (unfortunately) with recent history. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [December 6, 2016, 3:10pm UTC](https://boards.straightdope.com/t/why-the-mumps-outbreaks/774016/3 "2016-12-06T15:10:08Z")
It’s simple math. Vaccines aren’t perfect and they don’t need to be to protect everyone if a sufficient number participates. How many must be vaccinated depends on factors such as how contagious the disease is and how efficient the vaccine is. Now if, to grab some numbers out of the air, a disease affects 50 % of unvaccinated during an outbreak, and only 10 % of vaccinated, then if 95 % are vaccinated, 80% of the cases in the outbreak will be vaccinated. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [December 6, 2016, 5:55pm UTC](https://boards.straightdope.com/t/why-the-mumps-outbreaks/774016/4 "2016-12-06T17:55:19Z")
As noted, even a relatively high rate of protection (88% for two doses of mumps vaccine) means that a minority are still susceptible. Add in large numbers of people in close proximity (as on a college campus) and you have the potential for outbreaks. [The CDC](http://www.cdc.gov/mmwr/volumes/65/wr/mm6529a2.htm) is looking into whether a third dose of vaccine is effective. Currently the last MMR dose is routinely given at 4-6 years of age. While it’d be nice not to be concerned with mumps at all, we’ve still come a long way since before vaccination was available. In 1964 there were an estimated 212,000 cases of mumps in the United States. In the biggest outbreak year since then, there were about 3,500 cases. More often mumps cases number in the hundreds annually. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [December 6, 2016, 9:56pm UTC](https://boards.straightdope.com/t/why-the-mumps-outbreaks/774016/5 "2016-12-06T21:56:04Z")
Note that having larger numbers of unvaccinated kids, even if too young to go to college, allows those with inadequate vaccination responses to run into a kid with mumps somewhere and bring it back to the dorm. That’s a increasing pool of vectors so a lot more cases in general. If everyone was vaccinated, even if the vaccine wasn’t 100% effective, means that they’d be far fewer of these outbreaks. (Well, duh.) Herd immunity is a nice thing. ---
**Author:** ![Carryon](https://avatars.discourse-cdn.com/v4/letter/c/9fc29f/32.png) [@Carryon](https://boards.straightdope.com/u/Carryon)\ **Post date:** [December 8, 2016, 3:52pm UTC](https://boards.straightdope.com/t/why-the-mumps-outbreaks/774016/6 "2016-12-08T15:52:30Z")
Also vaccinations require exposure to keep them working. Here’s an example over simplified. If I get mumps vaccine and the first year it’s 99% effective, the next year it’s 95% effective. Ten years it’s 80% effective, in 20 years it’s 50% effective. Assuming during that time I DO NOT get exposed to mumps. But if I am in year two after I get my mumps vaccine, at it’s at 95% effectiveness and I am exposed to someone with mumps, then MY response gets boosted and I go back UP to 99% effective by the slight exposure and I don’t get mumps. The more people that get vaccinated decrease your chances of getting that exposure boost your immune system needs.