de Noronha TG, de Lourdes de Sousa Maia M, Ribeiro JGL, et al. - In view of the lower immune response to YF vaccine in children vs adults, researchers undertook this cross-sectional analysis to analyze children vaccinated in the first two years of life, to determine the duration of immunity to YF in those. Participants were children (n = 824) recruited in primary care units from a metropolitan area in Southeast Brazil, with ages between 9 months to 12 years, and having available vaccination records. Across time periods, a marked reduction in the proportion of seropositivity (95% C.I.) and geometric mean titers (GMT) (95% C.I.) was observed: from 86.7%, GMT 47.9 in newly vaccinated to 59.0%, GMT 14.8 and 42.2%, GMT 8.6, respectively in the subgroups vaccinated 31–72 months and 73–100 months before. According to the findings, there is a requirement for the revaccination of children residing in regions with yellow fever virus circulation in humans or in other primates, this observation is analogous to past revelations in adults. For those primarily vaccinated for yellow fever in the first two years of life, the change of a booster dose to 4 years of age was supported.