A modeling study predicts that changing long-standing U.S. guidance on hepatitis B vaccination at birth could substantially increase the number of young people who develop chronic hepatitis B virus (HBV) infections. The study estimates that delaying vaccination until age 2 months could make infants born in 2026 19% more likely to have chronic HBV by age 20, while a “shared clinical decision-making” approach could increase infections acquired by age 20 by 83%.
Previously, the Centers for Disease Control and Prevention (CDC) recommended that all newborns receive an HBV vaccine dose within hours of birth, a strategy known as universal birth-dose vaccination. In December 2025, the Advisory Committee on Immunization Practices (ACIP) recommended ending that policy for infants born to mothers who test negative for HBV, and the CDC accepted the recommendation.
How the guidance would change
Under the revised guidance, the birth dose would be recommended for infants whose mothers have tested positive for HBV or whose HBV status is unknown. Mothers who test negative would instead be advised to discuss with their doctors whether their babies should receive the dose at birth.
The CDC calls this approach “shared clinical decision-making.” The new recommendations state that infants who do not receive the birth dose should be at least 2 months old before beginning the HBV vaccine series. The recommendations have been widely criticized by health experts and have faced legal action.
The modeling study, published October 19 in the journal Annals of Internal Medicine, examined what could happen if the revised guidance is implemented.
“Overall, we think this modeling study has many strengths and provides an accurate prediction of how vaccine recommendations are likely to impact future chronic HBV in the United States,” Dr. Nora Terrault, a transplant hepatologist at the Keck School of Medicine of the University of Southern California who was not involved in the study, told Live Science via email.
More than 90% of HBV infections acquired during infancy or early childhood become chronic, according to the World Health Organization. Chronic HBV infection can lead to liver scarring, or cirrhosis; hepatocellular carcinoma, a type of liver cancer; and other chronic liver diseases. The CDC estimates that 15% to 25% of people with chronic HBV infection develop one of these serious liver conditions.
Modeling the effects of delayed vaccination
Study co-author Dr. Amir Mohareb, an infectious-disease physician and researcher at Massachusetts General Hospital and Harvard Medical School, and his colleagues built a simulation model using publicly available data. The model included current HBV prevalence, screening rates among pregnant women, the sensitivity of HBV tests, the proportion of children who complete vaccination by age 2, and the risk of chronic infection at different ages.
The researchers also estimated how often children might be exposed to HBV through contact with infected household or community members.
HBV is “very contagious,” Mohareb said. The virus can pass from mother to child during birth, but newborns can also be exposed to trace amounts of infected body fluids, such as blood from a wound. Babies who do not acquire HBV from their mothers can still become infected through contact with other family members or children if they are not vaccinated.
The researchers compared universal birth-dose vaccination with two alternatives: starting vaccination at age 2 months, and a more flexible shared-decision-making approach.
Compared with universal birth-dose vaccination, infants born in 2026 would be 19% more likely to have chronic HBV infection by age 20 if their first dose were delayed until 2 months of age.
The CDC guidance gives parents more discretion, stating that they should consult their child’s doctor to “determine when or whether to start their child on the hepatitis B vaccine series,” according to a CDC decision memo.
Mohareb’s team modeled both a fixed two-month delay and the less predictable shared-decision-making scenario. The researchers assumed that approximately 87% of children would complete the vaccine series by age 2 under the deferral strategy, compared with 50% under shared decision-making.
Mohareb said that other vaccines with similar wording in their recommendations had vaccination rates of only 25%. He emphasized that this part of the model is uncertain because it is unclear how the public will respond to the relaxed guidance.
At 50% vaccine-series coverage, the model projected an 83% increase in chronic HBV infections acquired by age 20. Under that scenario, approximately 50% to 70% of people born under the revised guideline would be susceptible to HBV infection at age 20, compared with fewer than 250,000 people under universal vaccination. The source article describes the affected age group as an annual population of approximately 1.8 million people.
“This represents a population at risk of acquiring HBV through sexual activity, drug use, etc., and these behaviors are more common among young people,” Terrault said.
A missed opportunity to prevent infection
To test how robust their findings were, the researchers varied the model’s most uncertain inputs across a wide range and ran the simulation 1,000 times. In every simulation, universal birth-dose vaccination reduced chronic HBV infections more than either alternative.
Mohareb said the conclusions appeared “robust” because “no matter how we change the numbers in the model, the conclusions are the same.” However, he noted that “the exact scale of the change will depend on how many people postpone getting vaccinated.”
The study did not estimate how many additional cases of liver disease or liver cancer might result from increased HBV infections. Terrault said the risks of liver failure, cirrhosis and liver cancer are “expected to increase because the opportunity to protect against infection is lost.”
Mohareb said he is not opposed to shared decision-making between doctors and patients. “They should always make decisions together,” he said. “But we don’t say we should rely on public health institutions to make decisions with patients, but rather to tell us what policies will make us healthier as a country.”
The number of pediatric HBV infections in the United States exceeded 25,000 per year in 1985. By 2024, the number of reported cases had fallen to fewer than 100. The decline has been attributed to HBV screening during pregnancy, antibody treatment for babies born to HBV-positive mothers, and universal birth-dose vaccination.
“Certainly, if universal vaccination recommendations are not followed, more hepatitis B infections will occur earlier in life,” Dr. Brian McMahon, a hepatologist and director of the Liver Disease and Hepatitis Program at Alaska Native Medical Center, told Live Science via email.
Study citation
Mohareb, A. M., Ganapathi, L., Dugdale, C. M., Rajbhandari, R., Ciaranello, A., Neilan, A. M., Jhaveri, R., Kim, A. Y., and Hyle, E. P. (2026). “Projected impact of the federally revised childhood immunization schedule in 2026 on chronic hepatitis B virus infection in the United States.” Annals of Internal Medicine.
This article is for informational purposes only and does not provide medical advice.
Source: www.livescience.com