Originally Posted by Jared Buffie
I'm certain he's referring to a relative risk reduction, not an absolute risk reduction. In other words, even a nonvaccinated person does not have a 100% chance of getting the mumps. For example (pulling numbers from my arse for illustration sake), a nonvaccinated person has a .1% chance of getting mumps, whereas a vaccinated person may have a .015% chance - so you're injecting all those toxins for an absolute risk reduction of .085%.
I'll take the otherwise minute chance of contracting a nonfatal disease while keeping those toxic ingredients out of my body. But I respect your choice, as well.
Your arse is a poor place to get numbers from.
The odds of a nonvaccinated person getting the mumps depends on whether everyone else is vaccinating or not. Before mass vaccination began in 1967, "estimates on infection rates var[ied] by subgroup from 100 to 6,000 per 100,000." This is an annual rate; the odds of you getting the mumps in your LIFETIME were nearly 100%. Nowadays, rates are around 30 per 100,000, as vaccination has made the bug no longer endemic in this country.
The odds of a vaccinated person getting the mumps depends on the strain used. The current version seems to see around 90% success rate with proper scheduling, although there seems to be some evidence that both natural nor vaccinated immunity may not be lifelong. Your odds are therefore around 10%, times either of the above rates, depending on whether or not you're willing to take advantage of everyone else's immunity in your hypothetical world.
I'll let you look at percentages on the varying severities of symptoms on your own.
All data from http://degreesofclarity.com/writing/mmr/