Relative efficacy of two acellular pertussis vaccines during three years of passive surveillance

Prolonged unblinded passive surveillance of the trial cohort from the Swedish 1986-87 pertussis vaccine efficacy trial indicates that a two-component vaccine, containing pertussis toxoid and filamentous haemagglutinin, provided better long-term protection against pertussis than a monocomponent pertussis toxoid vaccine. The relative risk (RR) for culture-confirmed pertussis was 1.5 (95% confidence interval (CI) 1.0-2.4), and RR for pertussis according to parents' diagnoses was also 1.5 (95% CI 1.1-2.1), for the monocomponent vaccine compared with the two-component vaccine.