Can the Measles, Mumps, and Rubella (MMR) vaccine be given to a 6-month-old infant and what are the potential side effects?

MMR Vaccination for 6-Month-Old Infants

The MMR vaccine should not be routinely given to 6-month-old infants but can be administered in special circumstances such as international travel or during measles outbreaks, with revaccination required at 12-15 months of age. 1

Indications for Early MMR Vaccination (6-11 months)

• MMR vaccine is generally administered only to children aged ≥12 months, as children younger than 12 months are less likely to develop adequate immunity when vaccinated with measles, mumps, and rubella antigens 1
• Early vaccination (at 6-11 months) is recommended in specific situations:
  • International travel to areas where measles is endemic 1
  • During measles outbreaks, especially if cases are occurring among infants under 12 months 1
• Monovalent measles vaccine is preferred for early vaccination, but MMR can be administered if the monovalent vaccine is not available 1

Efficacy and Immunogenicity of Early MMR Vaccination

• Children vaccinated before 8.5 months of age show markedly faster antibody decay and may lose protective antibody levels over time 2
• A study in Bangladesh showed that 94% of infants vaccinated at 6 months seroconverted for measles and rubella 3
• Children who receive MMR vaccine before their first birthday should be considered potentially susceptible to all three diseases and require revaccination 1

Revaccination Requirements

• Children vaccinated with MMR before the first birthday must be revaccinated with two doses of MMR 1:
  • First dose at 12-15 months of age (or at 12 months if the child remains in an area with high disease risk)
  • Second dose at least 28 days later
• This revaccination schedule is essential to ensure adequate protection 1

Side Effects of Early MMR Vaccination

• Early MMR vaccination is generally well-tolerated, with the lowest adverse event frequencies found in infants aged 6-8 months 4
• Common side effects include:
  • Local reactions at injection site (5-10% of infants) 4
  • Systemic reactions such as fever and fussiness (32-45% of infants) 4
• A review of adverse events after MMR vaccination in infants under 9 months did not identify any major safety concerns 5
• Parents of infants vaccinated at 6-8 months reported systemic adverse events less frequently (32%) than parents of children vaccinated at 9-11 months (45%) and 12-14 months (43%) 4

Special Considerations

• Infants aged less than 6 months are usually protected against measles, rubella, and mumps by maternally derived antibodies and ordinarily do not require vaccination 1
• For household contacts of measles patients, passive immunization with immune globulin (IG) may be preferred for infants under 12 months, as they are at highest risk for complications 1, 6
• During outbreaks in day care facilities, revaccination with MMR is recommended for all attendees and their siblings who have not received two doses of measles-containing vaccine on or after the first birthday 1

Important Caveats

• Early vaccination should be considered only when the risk of measles exposure is significant, as routine vaccination at 6 months is not recommended 1, 2
• The Centers for Disease Control and Prevention recommends that if within 72 hours of exposure, MMR vaccine can be administered to persons ≥6 months of age as post-exposure prophylaxis 6
• The Advisory Committee on Immunization Practices (ACIP) recognizes the use of MMR vaccine in infants aged 6-11 months as an off-label use 1