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 2787g (standard deviation=853g) and mean gestational age was 37.5 (standard deviation=3.08) weeks. The proportion that seroconverted was non-significantly higher in infants who weighed ≥2000g at birth (96.7%) than in those with birthweights <2000g (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.
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