Objective: To determine the immune responses of preterm infants(< 37 wks) to hepatitis B vaccine (HBV).

Methods: Study criteria included gestation of 25-37 wks and maternal hepatitis B surface antigen (HBsAg)-positive or unknown. 42 such infants received HBIG and vaccine (5 mcg Recombivax) during the first week of life; the 2nd (HBV-2) and 3rd (HBV-3) doses were given in accordance with AAP guidelines. Sera taken at 1-2 months after the HBV-3 were tested for antihepatitis B antibody by the ELISA technique. A titer of < 10 IU/ml was considered non-immune; between 10 and 100 IU/ml and >100 IU/ml were considered moderate and excellent responses, respectively.

Results: 5/42 infants were non-immune. These infants were born at ≤ 26 (n=2), 27, 32 and 36 weeks gestation. Of those who responded and were between 28 and 34 weeks gestation, 23 infants received the third dose after 7 months of age. Of these, 15 had excellent responses; of the 5 who received HBV-3 at less than 7 months, 1 had excellent response (p <.01).

Conclusion: 88% of preterm infants vaccinated according to current AAP recommendations responded after 3 doses of HBV. Infants ≤ 27 weeks gestation responded poorly. Delaying the 3rd dose of HBV until 7 months or later results in enhanced antibody responses.