Secondary analyses of the efficacy of two acellular pertussis vaccines evaluated in a Swedish phase III trial.

A placebo-controlled efficacy trial of two acellular pertussis vaccines carried out in Sweden in 1986-87 used culture confirmation as the principal case definition. However, the sensitivity of pertussis culture is low, and secondary analyses using more sensitive serological diagnostic criteria have therefore been carried out. These analyses confirm that vaccination with pertussis toxoid alone does protect against typical whooping cough with laboratory confirmation, but show that it does not protect against infection or colonization. There is evidence that the addition of filamentous haemagglutinin provides some protection against infection. Bacterial isolation rates were lower in vaccinated than unvaccinated children with serologically confirmed pertussis and increased with disease severity.