US cohort model projects hepatitis B rise after infant vaccination changes

A Markov cohort model estimated that recent changes to the US infant hepatitis B vaccination schedule could increase chronic infections and leave substantially more young adults susceptible to the virus. Compared with universal vaccination at birth, deferring vaccination until infants are at least two months old was projected to increase chronic hepatitis B virus infections by about 19%, while a shared clinical decision-making strategy was projected to increase infections by about 83%. These are model-based projections, not observed changes in infection rates following implementation of the new recommendations.

The policy sequence examined in the study began with a change from the Centers for Disease Control and Prevention’s prior recommendation of universal hepatitis B vaccination at birth. In December 2025, the Advisory Committee on Immunization Practices recommended deferred vaccination for infants whose mothers did not have hepatitis B until the infants were at least two months old. In January 2026, the CDC switched to recommending a shared clinical decision-making approach for those infants.

The source said the recommendations had been challenged by professional medical societies and public health agencies, but their clinical effects were unclear. The study, published in Annals of Internal Medicine , assessed the projected effects of these strategies rather than measuring outcomes under the new policies. Researchers from Mass General Brigham used a Markov cohort state-transition model to follow a synthetic population across health states over time.

The model was built with published epidemiological data and validated by comparing its projections with real-world CDC estimates of pediatric hepatitis B infections. It followed 3.6 million people, representing one year of births in the United States, through the first 20 years of life. Vaccination was recommended in every scenario for infants whose mothers were known to be hepatitis B positive.

The shared clinical decision-making scenario assumed that 50% of infants whose mothers were hepatitis B negative would be vaccinated at two months of age or later. The delayed-vaccination scenario assessed vaccination beginning at two months or later, while the comparison strategy was universal vaccination at birth. Under universal birth vaccination, the model projected that 255 people in the birth cohort would have chronic hepatitis B infection by age 20.

The count rose to 303 under delayed vaccination and 467 under shared clinical decision-making. These differences corresponded to projected increases of 48 and 212 chronic infections, or approximately 19% and 83%, respectively, relative to vaccination at birth. The model also projected a large difference in susceptibility at age 20: approximately 232,000 people would remain susceptible under universal birth vaccination, compared with about 474,000 under delayed vaccination and 1.8 million under shared clinical decision-making.

The study therefore projected both more chronic infections and a larger pool of susceptible young adults under each alternative to vaccination at birth. The authors emphasized the clinical importance of the projected increase in adult susceptibility. They said hepatitis B infections acquired in adulthood have a higher likelihood of leading to life-threatening conditions, including acute liver failure, and noted that hepatitis B is also a common cause of liver cancer.

Amir Mohareb, the study’s corresponding author, said in the research news release that even a small increase in childhood infections could have large clinical, public health and economic effects. Because the analysis is a model projection based on published data and specified vaccination assumptions, it does not establish how many infections will actually occur or how the recommendations will affect individual families. Its findings remain conditional on the model’s assumptions, including the 50% vaccination rate assigned to the shared clinical decision-making scenario and the accuracy of the input epidemiological data.

Subject of Research: Modeled effects of US infant hepatitis B vaccination schedule changes on chronic infections and susceptibility through age 20.

Article Title: Changes to hepatitis B immunization schedule would increase infections, model predicts

Article References: Changes to hepatitis B immunization schedule would increase infections, model predicts. Original publication (Bibliographic details unavailable.)

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Keywords: hepatitis B, HBV, infant vaccination, immunization schedule, cohort model, chronic infection, shared clinical decision-making, adult susceptibility, US births, public health, Changes, hepatitis