Objective. Preterm infants are at increased risk from infections and should be vaccinated at the usual chronological age. The aim of the study was to evaluate the immunogenicity and reactogenicity of a hexavalent diphtheria–tetanus–acellular pertussis–hepatitis B virus–inactivated polio and Haemophilus influenzae type b (DTPa-HBV-IPV/Hib) vaccine in preterm infants.

Methods. In a comparative trial, 94 preterm infants between 24 and 36 weeks (mean ± SD gestational age: 31.05 ± 3.45 weeks; mean birth weight: 1420 ± 600 g) and a control group of 92 full-term infants were enrolled to receive 3 doses of a DTPa-HBV-IPV/Hib vaccine at 2, 4, and 6 months. Immunogenicity was assessed in serum samples that were taken before and 4 weeks after primary vaccination. Evaluation of reactogenicity was based on diary cards.

Results. All preterm (n = 93) and full-term (n = 89) infants who were included in the immunogenicity analysis had seroprotective titers to diphtheria; tetanus; and polio virus types 1, 2, and 3. The immune response to the Hib and hepatitis B components was lower in preterm than in full-term infants: 92.5% versus 97.8% and 93.4% versus 95.2%, respectively. Vaccine response rates for pertussis antigens were >98.9% in both study groups. Although most geometric mean titers were lower in preterm infants, titers were similar for pertussis, a major threat for premature infants. The vaccine was well tolerated, and there were no differences in reactogenicity between groups. Some extremely immature infants experienced transient cardiorespiratory events within the 72 hours after the first vaccination with no clinical repercussion.

Conclusions. Preterm infants who were immunized with the hexavalent DTPa-HBV-IPV/Hib vaccine at 2, 4, and 6 months displayed good immune response to all antigens. The availability of this vaccine greatly facilitates the vaccination of premature infants.

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