Objective: To evaluate the safety and immunogenicity in adults of several different concentrations of an acellular pertussis vaccine.
Design: Double-blind, randomized, placebo-controlled trial.
Setting: Medical center immunization clinic.
Participants: One hundred eighteen healthy adult volunteers.
Interventions: Participants received standard adult tetanus-diphtheria vaccine alone or combined with full-strength, half-strength, or quarter-strength concentrations of a currently licensed acellular pertussis vaccine used for booster doses in young children. Full-strength vaccine contained 40 micrograms of pertussis proteins, consisting of 86% filamentous hemagglutinin, 8% pertussis toxin, 4% 69-kd outer-membrane protein, and 2% agglutinogens.
Main outcome measures: Local and systemic reactions were assessed for 14 days after vaccination. Serum samples for antibody assay were obtained before, 1 month after, and 1 year after immunization.
Results: Adverse reactions were few and minor and did not differ in frequency or severity among the four study groups. The groups receiving acellular pertussis vaccine showed strong antibody responses to pertussis antigens, which did not significantly differ by concentration of vaccine. After 1 year, levels of antibody to pertussis had declined by approximately 50% but remained substantially higher than preimmunization levels. The four groups did not differ in antibody responses to tetanus or diphtheria toxoids.
Conclusions: Routine reimmunization of adults with a vaccine containing acellular pertussis antigens in addition to diphtheria and tetanus toxoids can substantially enhance pertussis antibody levels without an increase in adverse reactions or diminution in response to the diphtheria and tetanus components. Such a program might materially reduce respiratory illness among both adults and children.