Response to hepatitis B vaccine in preterm infants: four-dose schedule.

The objective of this study is to test a four-dose Hepatitis B vaccine schedule in premature infants (PI) and assess the immunogenicity of the vaccine with this schedule. We studied 29 PI who received the vaccine against Hepatitis B at birth, 1, 5, and 9 months of age. Antibodies against surface antigen (Anti-HBs) were measured before the third and fourth doses and 12 weeks after the fourth dose. Levels higher than 10 mIU/mL were considered protective, whereas more than 100 mIU/mL was an excellent response. Twenty-nine PI were studied. The average weight at the time of the initial dose was 1398 g, gestational age of 32.5 weeks, and a postnatal age of 9 days. Since the initial measurement, protective levels were achieved in all patients. The response was excellent in 24.1, 75.9, and 89.7%, after the second, third, and fourth doses, respectively. No correlation was found between the type of response and the infants' weight or the postnatal age. The Anti-HBs geometrical levels were 51.9, 133, and 133 mIU/mL after the second, third, and fourth doses, respectively. The favorable results obtained might be due to: the four-dose schedule itself, the dose we used (10 microg), the time interval between the doses, and even a race factor. Our schedule seems to be useful for PI infants and probably is no longer necessary to delay the vaccination, although this should be confirmed by further studies.