Long term follow-up of vaccine trials is essential to establish the duration of protection. In the context of worldwide concern about rising pertussis incidence, estimates of antibody persistence after vaccination, which do not account for the rise in antibody due to natural boosting or infection, may overestimate the degree of protection afforded by pertussis vaccines. This was a 5year follow up study of a randomised controlled trial of diphtheria, tetanus, pertussis and polio booster vaccines in UK children aged 3.5-5years. Antibody persistence was measured at 1month, 1, 3, and 5years after vaccination and the kinetics of antibody decline were modelled longitudinally. Estimates of predicted antibody persistence 9years after the pre-school booster were derived from model parameters. Antibody levels 9years after vaccination were predicted to be above accepted thresholds for protection for diphtheria, tetanus and polio. Antibody responses to pertussis toxoid were undetectable in 49% of children at the 5year follow up visit, and responses were predicted to be undetectable in 69% (95% CI 45-88%) of children by the time of their teenage booster at 13-14years of age. There is no defined correlate of protection for pertussis. However, the large proportion of participants in this study with undetectable pertussis antibody levels at both measured and predicted timepoints suggests sub-optimal immunity in adolescence. Adding pertussis to the teenage booster for UK children as is done in other countries, would enhance immunity in adolescence.