Type-specific efficacy of acellular pertussis vaccine.

Two types of acellular pertussis vaccine have been used in Japan since their introduction in 1981. They are different in their antigen content and immunogenicity. To assess the type-specific efficacy of acellular pertussis vaccine commercially available in Japan, 442 households of patients with pertussis were surveyed from 1981 to 1987. The secondary attack rates in children 2 through 8 years of age were 61.3% (46/75) in unimmunized children, 7.5% (4/53) in children fully immunized by the filamentous hemagglutinin predominant type acellular pertussis vaccine, 14.3% (1/7) in children fully immunized by the pertussis toxin-filamentous hemagglutinin type vaccine, and 13.5% (7/52) in children given whole-cell pertussis vaccine. The estimated efficacy was 87.7% for the filamentous hemagglutinin predominant type vaccine and 76.7% for the pertussis toxin-filamentous hemagglutinin type vaccine in children aged 2 through 8 years. Both types of acellular pertussis vaccine were similarly effective, without any statistically significant differences, and their efficacy was not different from that of whole-cell vaccines. This survey also indicated that adults are a major source of infection, with a high secondary attack rate of 7.8%.