Problem: The reason that two measles, mumps, and rubella (MMR) vaccines at least a month apart are recommended is: The second dose of MMR "boosts" the immunity built from the first dose. Two vaccines 1 month apart is the standard dosing for all live virus vaccines. If the two MMR vaccine doses are given too closely together there is a greater likelihood of severe localized reaction to the vaccine. Only 95% of patients are fully immunized for measles after the first vaccine, with 99% having immunity after two doses of MMR. Need Assignment Help?