The Swedish efficacy trial of acellular pertussis vaccines--update and time for reflection

The trial cohort from the Swedish efficacy trial conducted during 1986-1987 is still under non-blinded surveillance. During post-trial follow-up until March 11, 1990, efficacy of the mono-component vaccine, JNIH-7, was estimated to be 65% (95% confidence interval, CI, 49-76%) and the efficacy of the two-component vaccine, JNIH-6, to 77% (95% CI 64-85%). For culture-confirmed cases with more than 30 days of cough efficacy for JNIH-7, was 79% (95% CI 66-87%) and for JNIH-6, 92% (95% CI 83-96%). The data indicate that two doses of acellular pertussis vaccine provide protection for 3 1/2 years or more. Continued analysis of data from the trial suggests that acellular pertussis vaccines protect against typical illness to the same extent as whole cell vaccines and that protection against infection may be augmented by adding one or more components to a pertussis toxoid-based vaccine. In spite of promising efficacy data, acellular pertussis vaccines are still not licensed outside Japan. The need for direct comparisons with efficacy and safety of whole cell vaccines will be discussed and salient problems of case definitions and case ascertainment in clinical trials will be emphasised.