Use of tetanus-diphtheria (Td) vaccine in children 4-7 years of age: World Health Organization consultation of experts.

For lifetime protection against diphtheria and tetanus, the World Health Organization (WHO) recommends six doses of diphtheria and tetanus containing vaccines. Td (reduced diphtheria toxoid, ≥2-5 IU) vaccines are currently licensed for ages 7 years and older, but use of Td vaccine for ages 4 years and older would have advantages for immunization programs in many low- and middle-income countries. For this reason, WHO convened an expert consultation to review the currently available evidence for the use of Td vaccine from 4 to 7 years of age which concluded: (1) no relevant biological difference in immune response in the relevant age group compared with children over 7 years of age; (2) adequate seroprotection in several studies with Td vaccine in the 4-7 age group and many studies using combination vaccines; (3) durable and protective response of at least 9-11 years duration in several longitudinal and modelling studies, (4) less reactogenicity compared with use of full-dose diphtheria vaccine, potentially improving the vaccination experience; and (5) adequate control of diphtheria in several countries using Td-containing combination vaccines in 4-7 year old children. On this basis, the experts concluded that from a programmatic perspective, Td vaccine given in ages 4-7 years, as a second booster dose in a six-dose series, would provide adequate protection against diphtheria and tetanus and recommended steps to include this change in age extension listed in the package insert.