The study was randomized, double-blind, and non-inferiority, conducted at two centers in Kenya and Uganda in infants aged 9-12 months without prior yellow fever vaccination.[1][2] 420 infants were enrolled, randomly assigned in a 1:1 ratio to standard vaccine dose (>13,000 IU) or a low-dose 500 IU dose from the Institut Pasteur de Dakar, given together with measles and rubella vaccine.[1][2] The primary outcome was seroconversion 28 days after vaccination, defined as a fourfold or greater rise in antibody titer as measured by the 50% plaque reduction neutralization assay.[1] In the per-protocol population, seroconversion was 99% (95% CI 96-100; 177 of 179 infants) with the standard dose and 93% (88-96; 166 of 179 infants) with the 500 IU dose.[1][2][4] The difference in seroconversion was -6.15 percentage points (95% CI -10.27 to -2.02), which did not meet the non-inferiority criterion for the 500 IU dose.[1][2] There were 12 serious adverse events reported in the study (8 in the 500 IU group and 4 in the standard group), all considered unrelated to vaccination.[1][2] The low-dose dose of 500 IU did not meet non-inferiority to the standard dose, so the standard dose is recommended for infants in the WHO routine immunization program.[1][2]