Ending the practice of immunizing all newborns against hepatitis B, as Health Secretary Robert F. Kennedy Jr. has recommended, would sharply increase the number of chronic infections and put more than half of Americans at risk of the disease by age 20, according to a new study published on Monday.
Hepatitis B is a highly contagious virus that can lead to cirrhosis, liver failure and liver cancer. To prevent infections, doctors in the United States have for decades administered the first dose of the hepatitis B vaccine to all babies within 24 hours of birth — and within 12 hours to infants whose mother is known to be infected.
But last December, a panel of advisers chosen by Mr. Kennedy recommended that parents should decide whether, or when, infants should get the shot if they were born to mothers who test negative for hepatitis B. In those cases, the group said, parents should decide “no earlier than 2 months of age.”
Mr. Kennedy and his associates have argued that hepatitis B is primarily a sexually transmitted disease and that babies do not need the protection unless their mothers are infected. But the virus can be spread by people who do not know they have it, as well as by household objects used by an infected person.
In January, Mr. Kennedy proposed a new childhood vaccination schedule in which the vaccine would be offered under a shared clinical decision-making approach — that is, after consultation with a health care provider.
In March, a federal judge temporarily blocked the implementation of both the December and January recommendations, restoring the universal hepatitis B birth dose as the official guideline from the Centers for Disease Control and Prevention. But the lawsuit continues and the final ruling may yet defer hepatitis B vaccination to two months of age or later.
“Overturning a longstanding immunization practice warranted evidence, and so that was the motivation to study this,” said Dr. Amir Mohareb, an infectious diseases physician at Massachusetts General Hospital and Harvard Medical School who led the study.
Dr. Mohareb and his colleagues modeled the potential impact of changing hepatitis B vaccination policy on the estimated 3.6 million infants born in a single year. Immunizing babies at 2 months of age rather than at birth would increase chronic hepatitis B infections acquired by age 20 by 19 percent, from an average of 255 cases per year to 303, the study found.
Switching to a shared decision-making policy would increase the number of chronic infections by 83 percent, to an average of 467 cases, and would result in more than 50 percent of children born each year entering adulthood susceptible to infection. The findings were published in the journal Annals of Internal Medicine.
The Department of Health and Human Services did not provide a comment on the results of the study or its implications.
The results are broadly consistent with those from two other studies published in April in the journal JAMA Pediatrics. One found that delaying vaccination until two months of age would lead to $16.4 million in added medical cost for infants born in one year. The second study found that preventing the increase in infections would require doctors to screen hundreds of thousands more pregnant women for hepatitis B than they currently do.
Together, the three studies underscore the idea that ending universal vaccination of newborns for hepatitis B would have grave consequences, said Dr. Noele P. Nelson, an author on the economic impact study, who helped summarize the current guidelines for the vaccine.
“We really could be headed for increased chronic hepatitis B viral infections in the United States if we continue on this path,” she said.
The new study suggests that the increase in new cases per year might be small, at least at first. But infections would quickly accumulate each year, greatly increasing the risk for anyone who is unvaccinated, noted Dr. José Romero, who led the Advisory Committee on Immunization Practices from June 2018 to August 2021, and the committee’s hepatitis B work group from 2017 to 2018.
In June 2025, Mr. Kennedy fired all 17 members of the A.C.I.P. and replaced them with new ones who mostly agreed with his skepticism of vaccines. Before making their recommendation to defer the birth dose, those members should have considered data from modeling studies to gauge the consequences, Dr. Romero said.
In fact, “a decision as monumental as this” would have merited multiple discussions among A.C.I.P. members when he was on the committee, and the potential for harm would have stopped them from recommending a change, he said: “There’s no question in my mind that they would have said no.”
Only about half of cases before 1991, when routine vaccination of newborns for hepatitis B began, were a result of transmission from an infected mother.
“If you think about how many children are in day care with other children, how many children are cared for by uncles, aunts and other guardians, it’s certainly a possibility to acquire the infection” from those others, Dr. Mohareb said. The virus could be spread by “something as simple as cutting the nails, because there could be microscopic blood on a nail clipper,” he added.
Some experts said they were concerned about making vaccines available only after a health care provider assesses a patient’s risk. That approach is appropriate when there’s uncertainty in the balance of risks and benefits from a vaccine, Dr. Nelson said.
But in the case of hepatitis B, there is no evidence of harm from the shots at any age. On the other hand, patients may not disclose risky behaviors, such as promiscuity or drug use, and doctors in turn may not screen for the disease because of constraints on time or resources.
“Informed consent is always part of the process, and the ability to ask questions also is always part of the process,” Dr. Nelson said. “But shared clinical decision making makes it look like the recommendation is weaker, and therefore is not followed as closely.”
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