Half-dose immunization for diphtheria, tetanus, pertussis: response of preterm infants.

The American Academy of Pediatrics currently recommends administering full-dose diphtheria, tetanus, pertussis, (DTP) vaccine to preterm infants, beginning at 2 months' chronologic age. Many physicians, however, continue to administer DTP vaccine at a reduced dosage in an attempt to lessen side effects. This study was designed to quantitate the immune response of 20 preterm infants immunized with half-dose DTP vaccine and to determine the nature and extent of side effects. Control subjects were 25 preterm infants immunized with full-dose vaccine. Although 96% of infants who received a full dose were able to mount a serologic response to pertussis after a second dose of DTP, 45% of infants who received a half dose were unable to mount a similar immune response to pertussis even after a third dose of DTP and required a full-dose (fourth dose of DTP) vaccine to better ensure protection. Serologic responses to diphtheria and tetanus were similar in the two groups. The incidence of side effects in preterm infants receiving both full-dose and half-dose DTP was less than that seen in a full-term population. Thus, the physician caring for the preterm infant should adhere to the American Academy of Pediatrics' recommendation for the immunization of preterm infants and offer full-dose DTP vaccine at the routine time intervals of 2, 4, 6, and 15 or 18 months' chronologic age to ensure adequate protection.