Response to the complete hepatitis B vaccine regimen in infants under 12 months of age: a case series

OBJECTIVES: Describing rates of seroconversion and its associated factors in a series of Brazilian infants following the final dose of the vaccine at 6 months of age. METHODS: Peripheral blood samples were collected after the third dose of the vaccine for the detection of anti-hepatitis B surface antibodies among infants of 7–12 months of age. We measured the association between seroconversion and birthweight, gestational age, time since administration of the vaccine in the maternity hospital and whether or not testing for hepatitis B surface antigen had been performed during pregnancy. RESULTS: We examined 40 infants. The mean birthweight was 2787 g (standard deviation = 853 g) and mean gestational age was 37.5 (standard deviation = 3.08) weeks. The proportion that seroconverted was non-significantly higher in infants who weighed ≥2000 g at birth (96.7%) than in those with birthweights <2000 g (80%, p = 0.149). There was no difference between the infants who were born at <37 weeks of gestational age and those born at ≥37 weeks (p < 0.178) neither between seroconversion and the time of application of the first dose of the vaccine after delivery (p = 0.202). CONCLUSION: The proportion of infants who seroconverted was similar to that found in other Brazilian studies. There were no differences in the proportion seroconverting by age at first immunization.