A retrospective cohort study presented at IDWeek analyzed laboratory and vaccination data for more than 158,000 children under age 5 in Kaiser Permanente Northern California. Among the 1.3% of children living in households with an active hepatitis B virus (HBV) carrier, 58.2% were exposed through someone other than their mother — such as a father, grandparent, or another household member. The study's lead author, Karen Jacobson, noted that even perfect identification of maternal infections would miss these alternative sources of exposure.
The findings come as the CDC's Advisory Committee on Immunization Practices (ACIP) voted in December to reverse a three-decade-old policy of universal HBV vaccination at birth for infants whose mothers test negative for hepatitis B surface antigen. Under the new guidance, those birth doses are left to shared decision-making, while infants of positive or unscreened mothers still receive a dose within 12 hours. Critics have warned this will lead to preventable infections; a recent modeling study projected an 83% increase in chronic HBV infections under the shared-decision approach.
Jacobson's study showed that 4.2% of children exposed to HBV by a non-maternal household contact were unvaccinated by age 30 days, within the two-month window ACIP now suggests for delaying the first dose. While 95% of birth-exposed infants were tested for HBV, only 3.6% of household-exposed children were tested. The study also found that household-exposed children were more likely to be vaccinated than unexposed peers (93.5% vs. 86.7%), suggesting some families recognized the risk.
The authors caution that the 1.3% household exposure rate is likely an underestimate, since it relied on household contacts being Kaiser Permanente members and on accurate address data. The study could not determine whether exposed children actually developed HBV infections, but infection in infancy carries a high risk of chronic disease. The results underscore that focusing solely on maternal screening may leave a meaningful gap in protecting young children from hepatitis B.