More than half of children younger than 5 living with someone with active HBV infection had potential exposure through a household member other than their birth mother, according to a retrospective cohort study within Kaiser Permanente Northern California presented at IDWeek 2026.
Karen Jacobson, MD, MPH, an infectious diseases physician and research scientist at the Vaccine Study Center at the Kaiser Permanente Division of Research, said that young children can acquire the virus through close interpersonal contact, including contact with household members.
“Maternal hepatitis B screening alone does not identify all potential sources,” said Dr. Jacobson. “Our study highlights the importance of being very comprehensive in how we think of exposures and knowing that the risk is not just limited to that perinatal period."
The study sought to characterize potential exposure beyond maternal infection amid discussions about which infants should receive hepatitis B vaccination at birth.
In December 2025, CDC changed its universal recommendation for HBV vaccination at birth to routinely recommend the birth dose only for infants born to mothers with active HBV infection or unknown HBV status. For infants whose mothers test negative, parents and clinicians may choose vaccination at birth or defer it through shared decision-making. If deferred, CDC suggested beginning vaccination no earlier than 2 months of age.
Study methods and findings
The study included 158,169 children younger than 5 as of June 16, 2023, living in 131,800 households. To be included, children had to be linked to their birth mother through electronic medical records and share a street address with at least one other Kaiser Permanente Northern California member on that date.
Children were classified as birth-exposed if their birth mother was a household contact with active infection, household-exposed if only a contact other than their birth mother had active infection or unexposed if no household contact with active infection was identified.
The researchers identified 2,024 children (1.3%) living with at least one person with active HBV infection. Among these children, 846 (41.8%) were classified as birth-exposed and 1,178 (58.2%) as household-exposed. Overall, 1,689 households included someone with active infection. Among household contacts other than birth mothers who had active infection, 76.5% were male.
Vaccination and testing patterns
Early vaccination coverage differed by exposure group. All birth-exposed children received hepatitis B vaccination within 7 days of birth, compared with 93.5% of household-exposed children and 86.7% of unexposed children. Dr. Jacobson reported that 97% of children eventually received at least one dose. However, 4.2% of household-exposed children remained unvaccinated at 30 days, and some had not received a dose by the end of follow-up.
Testing also differed across groups. According to Dr. Jacobson, 95% of birth-exposed children underwent hepatitis B testing, compared with 3.6% of household-exposed children and 0.4% of unexposed children.
The study had several limitations. Because children were not routinely screened, the researchers did not know whether any household-exposed children became infected. Other limitations included potentially inaccurate addresses and an inability to identify household contacts with active infection who were not health system members or had never been tested. The study also could not capture potential exposures outside the household, and its findings may not generalize to other U.S. populations.
Funding and potential conflicts of interest were not provided.