This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax firstname.lastname@example.org with numerous contributions by others.
The Merck Manual estimates its effectiveness at 95%. The Physician's
Desk Reference gives its effectiveness as 96%. Switzerland has gotten
lower efficacy rates, for mumps, out of its strain of the MMR vaccine,
and Swiss scientists have been comparing the efficacy of different
strains to improve this situation (Swiss Medical Weekly,