Acellular Pertussis Vaccine Efficacious in Adolescents and Adults

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Summary and Comment

Acellular Pertussis Vaccine Efficacious in Adolescents and Adults

Routine use of such a vaccine in adults and adolescents could reduce pertussis incidence in children.

Pertussis incidence is increasing among adolescents and adults in the U.S. due to waning vaccine- or infection-induced immunity. Infected adolescents and adults can transmit Bordetella pertussis to infants, who are especially vulnerable to severe pertussis. In the randomized, double-blind Adult Pertussis Trial, conducted at eight U.S. sites, researchers prospectively evaluated the efficacy of an acellular pertussis vaccine administered to healthy 15- to 65-year-olds from 1997 through 1999.

The 2781 participants received an acellular pertussis vaccine (in a dose one third of that given to children) or a hepatitis A vaccine (control). Then, they were followed for up to 2.5 years (median, 22 months) for illnesses with cough lasting >5 days. Such illnesses were evaluated by culture and PCR of nasopharyngeal aspirates and by serologic tests.

Cases of illness with prolonged cough (n=2672) were evenly distributed between the study groups. Ten cases of laboratory-confirmed pertussis occurred (9 of them in controls), yielding an overall vaccine efficacy of 92%, adjusted for the duration of illness. Pertussis incidence in the control group was 370 to 450 cases per 100,000 person-years, depending on the case definition, which translates to about a million cases annually in the U.S. among individuals $≥$ 15 years old. Laboratory-confirmed pertussis accounted for 0.7% to 5.7% of illnesses with prolonged cough, depending on cough duration.

Comment: Optimal control of pertussis will probably require immunization of adolescents and adults as well as children, and this definitive study now shows that acellular pertussis vaccine is highly efficacious in individuals $≥$ 15 years old. Two acellular pertussis vaccines formulated for adults (and combined with an adult formulation of diphtheria and tetanus toxoids) are now licensed in North America and Europe. As an editorialist points out, these vaccines should be widely used in place of the traditional diphtheria and tetanus vaccines for adolescents and perhaps also for adults.

— Neil R. Blacklow, MD

Published in Journal Watch Infectious Diseases November 4, 2005