This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax firstname.lastname@example.org with numerous contributions by others.
The Merck Manual and the Physician's Desk Reference estimate its
effectiveness at 95%. This estimate is based on studies of the
immunity induced by a series of vaccinations beginning at 15
months. Another article, estimating the immunity induced in field
conditions (including some Third World countries, which may have less
reliable vaccine storage) by a series of injections beginning at 9
months (the injections are started earlier in areas where measles is
widespread), estimated effectiveness as 85% (Clements, Strassburg,
Cutts, and Torel).
A recent article in Pediatric News (Imperio. Vaccine-Exempt At Higher
Risk For Measles. Pediatric News 33(9):9, 1999.) reported that
"Individuals aged 5-19 years who were not vaccinated due to religious
or philosophical exemptions were, on average, 35 times more likely
than vaccinated individuals to contract measles, according to a
population-based, retrospective cohort study."