A randomised double-blind clinical trial of two yellow fever vaccines prepared with substrains 17DD and 17D-213/77 in children nine-23 months old|
Collaborative Group for Studies of Yellow Fever Vaccine
This randomised, double-blind, multicentre study with children nine-23 months old evaluated the immunogenicity
of yellow fever (YF) vaccines prepared with substrains 17DD and 17D-213/77. YF antibodies were tittered before
and 30 or more days after vaccination. Seropositivity and seroconversion were analysed according to the maternal
serological status and the collaborating centre. A total of 1,966 children were randomised in the municipalities of
the states of Mato Grosso do Sul, Minas Gerais and São Paulo and blood samples were collected from 1,714 mothers.
Seropositivity was observed in 78.6% of mothers and 8.9% of children before vaccination. After vaccination, seropositivity
rates of 81.9% and 83.2%, seroconversion rates of 84.8% and 85.8% and rates of a four-fold increase over
the pre-vaccination titre of 77.6% and 81.8% were observed in the 17D-213/77 and 17DD subgroups, respectively.
There was no association with maternal immunity. Among children aged 12 months or older, the seroconversion
rates of 69% were associated with concomitant vaccination against measles, mumps and rubella. The data were not
conclusive regarding the interference of maternal immunity in the immune response to the YF vaccine, but they suggest
interference from other vaccines. The failures in seroconversion after vaccination support the recommendation
of a booster dose in children within 10 years of the first dose.
yellow fever vaccine; randomised clinical trial; immunogenicity