A Diagnostic Challenge: Neonatal Post Immunization Hepatitis B Antigenemia in the Infant with no Prenatal Care

Background: Perinatal infection with Hepatitis B virus can lead to long-term complications associated to chronic liver disease. Neonatal vaccination has been shown to effectively reduce the incidence of chronic HBV by 90%, especially in infants born with no prenatal care.

Objective: To report a case of post immunization Hepatitis B antigenemia in an infant born to a mother with unknown pregnancy.

Methods: Medical record review.

Results: The infant was born at 40 weeks of gestational age as per Ballard Assessment to a 29-year-old Grava 3 Para 2 mother with no prenatal care. He was transferred to our institution on the same day of birth with a weight of 3340g. At the moment of transfer, the mother’s HBsAg status was unknown. Hepatitis B vaccine was administered to the infant at 1hr-old at the referring institution. Both infant and mother were screened with Hepatitis profile. The infant had a positive HBsAg test at 48hrs-old, which was verified. Due to unknown result of recent maternal HBsAg test, the infant was given HBIG at 7 days old. HBsAg and HBsAb were repeated 24hrs later and were both non-reactive. These findings are most suggestive of Post Immunization Hepatitis B Antigenemia.

Conclusion: Transient antigenemia is a rare consequence of Hepatitis B vaccination. In the setting of babies born with no prenatal care, these results need to be interpreted carefully to consider false positive results versus perinatal HBV transmission versus this phenomenon. In the case of our patient, mother’s negative test results were available when patient was 10 days old. Transient Hepatitis B Antigenemia has been described before as early as at 16 hours-old post vaccination. It is important to have the mother’s test results or perform HBsAg test to infants before they are vaccinated to avoid unnecessary testing to our patients.