September 1996
ROCKVILLE, Md. — The Food and Drug Administration (FDA) approved the first diphtheria-tetanus-acellular pertussis (DTaP) vaccine for the infant series.
Tripedia (Connaught Laboratories) may now be used for the primary immunization series at 2 months, 4 months and 6 months of age. Because it was approved in 1992 for the fourth and fifth doses at 15 months to 18 months and 4 to 6 years, it is immediately available.
Unlike whole-cell vaccines, which contain the complete pertussis bacterium, acellular vaccines contain only those proteins that are thought to be necessary to confer immunity. Acellular vaccines may contain from one to five proteins; Tripedia contains two (pertussis toxoid and filamentous hemagglutinin). The acellular component is manufactured by The Research Foundation for Microbial Diseases of Osaka University (Biken).
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The efficacy rate of three doses of Tripedia was 94% when pertussis was defined as paroxysmal cough lasting 21 days or longer. When pertussis was defined as any cough lasting 21 days or longer, the efficacy rate was 81%. The efficacy rates for a German whole-cell vaccine were 97% and 94%, respectively, according to the Centers for Disease Control and Prevention.
Studies found Tripedia to be less reactogenic than whole-cell pertussis vaccines. Local and systemic reactions were lower among children who received the acellular pertussis product than those who received whole-cell vaccine.
Because DTaP vaccines are less reactogenic than whole-cell vaccines, it is hoped that their licensure for the infant series will help boost immunization rates.
In the early 1980s, immunization rates fell after reports of serious neurologic events allegedly associated with DTP vaccines. No connection between DTP vaccination and rare neurologic events has been proved, however.
In anticipation of licensure, the Advisory Committee on Immunization Practices (ACIP) is drafting recommendations for using DTaP for the first three doses.
Although the statement has not been finalized, the ACIP clearly states a preference for acellular pertussis vaccines over whole-cell products.
"DTaP vaccine has been shown to be highly efficacious when administered as the primary series during infancy and is preferred for all five doses in the schedule because it substantially reduces the frequency of local reactions, fever and other systemic events that frequently follow receipt of whole-cell DTP," the draft statement reads. "DTaP is also preferred for all remaining doses in the schedule for children who have started the vaccination series with one, two, three or four doses of DTP. ... During the transition from use of whole-cell DTP to DTaP, DTP is an acceptable alternative to DTaP for any of the five doses. DTP combined with Haemophilus influenzae type b conjugate vaccine (DTP-Hib) is an acceptable alternative to DTaP and Hib vaccine administered at separate injection sites and has the advantage of requiring fewer intramuscular injections."
Tripedia is contraindicated in children who have an immediate anaphylactic reaction or encephalopathy temporally associated with a previous dose and not due to another identifiable cause.
Other DTaP vaccines are in various stages of review for licensure, and an application for a DTaP-Hib combination vaccine was recently filed with the FDA.
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