This is a phase IIb clinical trial investigating the non-inferiority of immune responses in children given two doses of measles vaccine at different timepoints. The study will randomise 450 children to 3 groups: group A will receive measles containing vaccine (MCV) at 6 and 12 months ; group B at 9 and 18 months; Group C at 6 and 18 months.

Two doses of measles containing vaccine (MCV) are recommended in young children with the first dose given at different times depending on the setting. In low-incidence settings the MCV1 is given at 12 months of age or later as more infants over 12 months of age respond to MCV1 due to the absence of maternal antibody interference and an overall better immune response due to the maturation of the infant immune system. In high measles incidence settings MCV1 is given earlier at 9 months of age as there is no remaining protection from maternal antibody at this age and risk of infection if unvaccinated can be high. However, in children born with low levels or rapid decay of maternal antibody, the 9-month timing for MCV1 means the infant may be susceptible to infection for some months prior to vaccination. Therefore, in settings of high infant measles incidence, an early first dose at 6 months of age may bridge this susceptibility gap.

Our study will assess differences in protective levels of measles antibody in children randomised to receive early (6 months) or standard (9 months) MCV1 in a high incidence measles setting, and early (12 months) or standard (18 months) booster vaccines, in those who are given early MCV1. There will be 5 blood draws over 2 years. The study will compare children who received a) two doses of measles vaccine at 6 and 18 months with 9 and 18 months, and b) two doses of measles vaccine at 6 and 12 months compared with 6 and 18 months.

The study is funded by the Bill & Melinda Gates Foundation (INV-048650)

1. Trial Participants Children aged 6 months (23 - 28 weeks) at time of screening

2. Inclusion Criteria

   • Aged 6 months (23 - 28 weeks) at time of screening
   • Received all previous vaccines as per country Expanded Programme of Immunization (EPI) schedule, verified by child health card
   • Parents/caretakers willing to give informed consent for their and their children's participation and stay in the geographical area where the study would be conducted

3. Exclusion Criteria

The participant may not enter the trial if any of the following apply:

• Child not healthy enough to be vaccinated in the opinion of the investigator
• Recent family history of measles infection (since birth)
• Previous receipt of any measles vaccination
• A family history of congenital or hereditary immunodeficiency other than HIV
• Receipt of more than 1 week of immunosuppressant or immune modifying drugs e.g. high dose steroids.
• Major congenital defects or serious chronic illness that in the opinion of the investigator are likely to modify immune responses or the ability to comply with the requirements of the study.
• History of any neurological disorders or seizures
• Administration of immunoglobulins and/or any blood products since birth or planned administration during the study period
• Other abnormalities or medical history that contraindicated measles vaccination

All participants receive the same vaccines but are randomised to the timing of administration of the vaccines.