Area of Science:

• Pediatrics
• Immunology
• Public Health

Background:

• Measles, Mumps, and Rubella (MMR) vaccine is typically licensed for administration starting at 9 months of age.
• Off-label use of the MMR vaccine in infants aged 6-9 months is common during measles outbreaks or for travel to endemic areas.
• Published literature on MMR vaccination in this younger age group is limited and comprises small-scale studies.

Purpose of the Study:

• To review existing literature on the immunogenicity and safety of the MMR vaccine in infants aged 6-9 months.
• To evaluate the evidence supporting early-life MMR vaccination in specific epidemiological contexts.

Main Methods:

• Systematic review of published literature focusing on MMR vaccination in infants under 9 months.
• Analysis of studies assessing immune responses (antibody titres, T cell responses) and vaccine safety profiles.

Main Results:

• Infants vaccinated before 9 months demonstrated lower antibody titres compared to older infants.
• T cell responses against measles were comparable between the early and standard vaccination groups.
• The safety profile of the MMR vaccine in infants aged 6-9 months did not significantly differ from that in infants vaccinated at or after 9 months.

Conclusions:

• Early-onset MMR vaccination (from 6 months) may be considered when the risk of measles infection outweighs the benefits of waiting for standard vaccination.
• The decision to vaccinate earlier should be based on a risk-benefit assessment considering the likelihood of exposure and disease severity.
• Further research with larger cohorts is warranted to fully elucidate the long-term efficacy and optimal timing of MMR vaccination in infants.