A child who received the MMR vaccine at 9 months now needs to enter Kindergarten at age 4. How many additional doses of MMR should he receive?

The child in this scenario received the MMR (measles, mumps, and rubella) vaccine at 9 months of age. According to the CDC immunization schedule, the MMR vaccine is typically administered in two doses, with the first dose given between 12 to 15 months of age and the second dose between 4 to 6 years of age.

Given that the child was vaccinated at 9 months, that dose does not fulfill the requirement for the first dose as per the standard immunization schedule. Therefore, when the child turns 4 years old and prepares to enter Kindergarten, they would need to receive the first dose of MMR at the appropriate time, followed by the second dose.

Consequently, the child would require one additional dose of the vaccine at age 4 to meet the requirements for school entry. The initial dose at 9 months does not count toward the two-dose requirement, thus leading to the conclusion that only one additional dose is needed.