Answers to questions about the acellular pertussis vaccine.

Two acellular pertussis vaccines, which are usually combined with diphtheria and tetanus toxoids, are now licensed for use in the United States. These vaccines are immunogenic and produce fewer adverse reactions than whole-cell pertussis vaccines. At present, acellular vaccines are to be used only for the fourth and fifth booster doses of diphtheria-tetanus-pertussis vaccine in children 15 months of age or older. Efficacy of the acellular vaccines in younger children is currently being investigated.