What’s Happening with the MMR Vaccine?

What’s Happening with the MMR Vaccine?: The fact that 44.4 percent of secondary measles cases in the Colorado outbreak occurred in individuals who had received two documented doses of MMR vaccine stands in stark contrast to the expected vaccine failure rate. The MMR vaccine is widely cited as having ~94 percent effectiveness after two doses, meaning that only 6 percent of fully vaccinated individuals are expected to remain susceptible under typical exposure conditions.