http://www.cdc.gov/vaccines/vpd-vac/rubella/default.htmMost children who get the vaccine develop immunityto all three diseases (over 99% for measles and 95% for mumps and rubella). Protectionis believed to be life-long. Two doses of vaccine are recommended, with the first dose given at 12–15 months of age. The second dose may be given 4 weeks after the first, but it is usuallygiven at 4–6 years....How effective is this vaccine?Approximately 95% of individuals become immune to rubella after a single dose of vaccine. The second dose of MMR vaccine is intended to produce immunityin the 5% of persons who did not respond to the first dose.