Pertussis re-emerged in Sweden with a cumulative incidence of about 60% during the first 10 years of life, when the locally produced cellular
vaccine lost its efficacy around 1970 and general vaccination was discontinued in 1979. The epidemiology, clinical features, and immunology of
pertussis and a monocomponent
pertussis toxoid vaccine were studied in Göteborg, Sweden. After phase 1 and 2 studies, a randomized, double-blind, placebo-controlled trial of
pertussis toxoid (PTox), compounded with
diphtheria and
tetanus toxoids, was administered to 3450 children according to the Swedish schedule at 3, 5, and 12 months of age. After a mean follow-up of 18 months, the efficacy was 71% overall and 75% in household contacts, respectively. A statistically significant correlation was found between the level of PTox-induced
antibodies and protection against
pertussis. As observed with cellular and with multicomponent
acellular vaccines, PTox reduced the severity of disease and the percent of children with positive cultures. Furthermore, vaccination reduced the transmission of Bordetella pertussis to household contacts in the vaccinees compared with the controls who received only
diphtheria and
tetanus toxoids. Patients with culture-verified Bordetella parapertussis
infection reacted with
antibodies to
pertactin and to filamentous
hemagglutinin but not to
pertussis toxin, and some subsequently developed
pertussis. The antibody responses of patients with
pertussis to the surface
polysaccharides of B
pertussis and to B parapertussis were cross-reactive serologically. Serosurveys showed that only
antibodies to
pertussis toxin were related to the occurrence of
pertussis in the general population:
antibodies to filamentous
hemagglutinin and
pertactin were probably stimulated by
antigens of other bacteria as well as Bordetellae. Mass vaccination of Göteborg children born in the 1990s was started in 1995. In February 1999, about 55% had been vaccinated and both B
pertussis and
pertussis decreased significantly in individuals of all ages (herd immunity). Similar to
diphtheria, PTox-induced immunity to
pertussis occurs both on an individual and community basis. The apparent greater efficacy of multicomponent acellular
pertussis vaccines compared with monocomponent PTox was proposed to be an artifact created when the diagnosis of
pertussis was made by the serologic criteria of the World Health Organization only. Our conclusion is that PTox is both an essential and alone sufficient
antigen in acellular
pertussis vaccines.