Delaying newborn hepatitis B shots could raise chronic infections by 19%, study finds

A model of 3.6 million US births projects more chronic infections if the first dose is delayed, with risks rising further if fewer babies are vaccinated.

Scrapping the universal hepatitis B shot for newborns could lead to a sharp rise in chronic infections among American children, according to a modelling study published in the Annals of Internal Medicine. The research comes as the Trump administration’s health policy shift on infant vaccination has reopened a long-running debate over whether babies whose mothers test negative should still receive a dose at birth, or wait until later. The study looked at one U.S. birth cohort of roughly 3.6 million babies and found that the lower the vaccination rate, the greater the projected harm.

Hepatitis B is often described as a silent infection because it can spread without immediate symptoms, sometimes passing from mother to child at birth or through infected blood before liver damage becomes apparent. Public-health experts have long warned that infection in infancy is especially dangerous: Johns Hopkins says up to 90% of babies infected in the first year of life develop chronic disease, and untreated early infection carries a substantial lifetime risk of liver cancer. That is why many paediatric and infectious-disease specialists have treated the birth dose as a backstop, particularly when maternal infection is missed or documentation is incomplete.

According to the study, delaying the first dose until two months of age would raise chronic infections by 19% under the authors’ base-case assumptions, while a shared-decision approach could increase them much more if uptake falls. The paper also stresses that these are projections, not observed cases, but the scale of the cohort makes even small changes consequential. Dr Amir Mohareb, the study’s lead author and an infectious-disease researcher at Harvard Medical School and Massachusetts General Hospital, told TIME that the issue matters because the consequences would not be a one-off event but something that could repeat year after year.

The new modelling adds to a growing body of evidence that the revised schedule could carry medical and economic costs. A separate analysis, also published this year, estimated that delaying vaccination could leave infants with more acute and chronic infections, more hepatitis B-related deaths and an added $16.4 million in health-care spending for a single birth cohort. The American Academy of Pediatrics continues to recommend vaccination within 24 hours of birth, and in its response to the CDC’s 2025 decision it warned that paediatricians were already seeing signs that some parents were declining the shot. Meanwhile, the CDC says infants whose mothers test positive or whose status is unknown should still receive the vaccine within 12 hours of birth, while the rest may now wait until at least two months if parents and clinicians decide to defer it.