Kaiser Permanente Study: 58% of Children Exposed to Hepatitis B at Home Were Exposed Through Someone Other Than Their Mother

Since the CDC's Advisory Committee on Immunization Practices (ACIP) voted in December 2025 to stop recommending a universal hepatitis B birth dose for babies of mothers who test negative, and days after a modeling study projected more chronic infections under that change, a new real-world analysis points to where the exposure actually comes from.

The retrospective cohort study was presented at the IDWeek annual meeting by Karen Jacobson, MD, MPH, of the Kaiser Permanente Vaccine Study Center in Pleasanton, California. It covered 158,169 children younger than 5 in Kaiser Permanente Northern California, using lab and vaccination data through March.

Most household exposure did not come from mothers

Of the children studied, 1.3% lived in a household with a person who had active hepatitis B infection. Among those exposed children, 58.2% were exposed through a contact who was not their mother. The other 41.8% were exposed through their mothers.

"Our findings show that even if it is possible to accurately identify every single maternal infection, this would not account for potential exposure to an infected father, grandparent, or another person living in the household," Jacobson said at a press briefing before the meeting.

The study measured exposure, not confirmed infection in the children. Jacobson also said transmission to children from non-maternal sources is currently quite rare in the U.S. because vaccination rates are high. "But if rates decrease, more infants could be at risk," she said.

The 2-month gap

Under the ACIP change, babies of mothers who test negative for hepatitis B surface antigen get shared decision-making between parents and clinicians. If a family skips the birth dose, the first shot is pushed to at least 2 months of age.

That window matters in Jacobson's data. Of children exposed to hepatitis B by a non-maternal household contact, 4.2% were unvaccinated at 30 days old, which falls inside the delay period.

Testing looked very different depending on how a child was exposed. About 95% of infants exposed at birth through their mothers were tested for the virus, and all were vaccinated within 7 days of birth. Only 3.6% of children with household exposure were tested.

That gap means the study cannot say how many household-exposed children went on to be infected.

Vaccination was higher among exposed children: 93.5% of those with household exposure were vaccinated, versus 86.7% of those without. Jacobson said this suggests some families or providers recognized the risk.

"ACIP's latest recommendations are really focusing on that maternal exposure, and I think it's important that other sources of potential exposure are not ignored," she said.

What ACIP kept, and the argument behind the change

ACIP still recommends a birth dose within 12 hours of delivery for infants born to mothers who test positive or whose status is unknown. The change applies only to babies of mothers who tested negative.

Supporters of the new approach, described as allies of Health Secretary Robert F. Kennedy Jr., argue the virus spreads primarily through sexual contact and that babies of uninfected mothers do not need immediate protection. The Kaiser data is a direct counterpoint: it identifies non-maternal household members as the larger share of exposure in young children, though the study does not address sexual transmission.

Critics have warned the change will cause preventable acute and chronic infections, liver cancers and deaths, plus millions of dollars in added health costs. A separate modeling study cited in that debate put the increase in chronic infections under shared decision-making at 83%.

The Annals of Internal Medicine simulation covered in our earlier reporting modeled 3.6 million children born in a single year. It projected chronic infections rising 19% if 75% of infants got a delayed first dose, and 225% if only about 26% did. An author of the study, Amir Mohareb of Harvard Medical School and Massachusetts General Hospital, said the modeling covers a single birth year.

Refusals were already rising

A JAMA Network Open study of 93,163 newborns at three University of Pennsylvania health system centers found that refusals of the newborn hepatitis B vaccine more than doubled from 2018 to 2025. In all, 9,400 newborns, or 100.9 per 1,000, did not receive the vaccine.

The researchers found that 83% of newborns whose parents refused vitamin K prophylaxis also had the hepatitis B vaccine refused. They said this likely reflects parents who decline one preventive intervention often declining others.

That is one health system, and the data predates any effect from the December ACIP vote on parents' choices.

The fight continues

The American Academy of Pediatrics continues to recommend a birth dose for all infants. Fifteen states have sued the Trump administration over changes to the vaccine schedule. A federally funded hepatitis B vaccine trial in newborns has also drawn more pushback, according to the CIDRAP and Unbiased Science vaccine-policy series.

The unresolved question is how many families will take the delayed option, and whether anyone will be testing household contacts closely enough to find out. In Jacobson's cohort, 96.4% of children with household exposure were never tested.

The states' lawsuit remains pending.