Absolute efficacy of acellular pertussis vaccines in household settings.

Household studies in the two recently concluded Swedish pertussis vaccine efficacy trials demonstrated that one monocomponent and one five-component candidate acellular pertussis vaccine had reasonably good protective efficacy against clinically typical pertussis after household exposure. Another recently concluded German household study, led from Mainz, also demonstrated reasonably good efficacy for a three-component acellular pertussis vaccine. The methods of case ascertainment and duration of follow-up had a marked influence on the efficacy estimates of another candidate two-component acellular pertussis vaccine. This vaccine and a U.S. licensed commercial whole-cell vaccine had very low efficacy against pertussis infection after household exposure. Differences in methodology preclude direct comparisons between the efficacy estimates obtained in various household studies.