Immunogenicity of hepatitis B vaccine in preterm and full term infants vaccinated within the first week of life.

The immunogenicity of a Hepatitis B vaccine was evaluated in 110 neonates (57 full term and 53 preterm) born to Hepatitis B surface antigen (HBsAg) negative mothers. Three 10 microg doses of recombinant Hepatitis B vaccine were administered: the first dose within the first week of life; the second between 1 and 2 months; and the third at 5-7 months of age. Anti-HBs antibody titres were measured 3 months after the third dose. The seroconversion rate in preterm infants (77%; 95% CI=64.7-87.1) was significantly lower than in full term infants (98%; 95% CI=91.6-99.9) while the mean anti-HBs titres among those infants that did seroconvert was lower in preterm (186.6 mIU ml(-1)) than in full term infants (537.5 mIU ml(-1)). More full term than preterm infants showed titres greater than 100 mIU ml(-1) (71.9 and 41.5%, respectively). We conclude that the administration of a recombinant Hepatitis B vaccine shortly after birth is less immunogenic in preterm infants weighing <1800 g at birth than in full term infants. Currently accepted recommendations for post exposure perinatal prophylaxis may be inadequate to protect preterm infants.