FILE PHOTO: U.S. Health and Human Services Secretary Robert F. Kennedy Jr., testifies before a Senate Finance Committee hearing on President Donald Trump's 2026 health care agenda, on Capitol Hill in Washington, D.C., U.S., September 4, 2025. REUTERS/Evelyn Hockstein/ File Photo

By Michael Erman

ATLANTA (Reuters) - U.S. vaccine advisers are poised on Thursday to vote on changes to the nation's childhood immunization schedule, signaling one of the most consequential policy moves under Health Secretary Robert F. Kennedy Jr. that medical experts have said would expose many more Americans to preventable illnesses.

The changes are being considered by the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices. Its chairman, Martin Kulldorff, opened the two-day meeting in Atlanta with a defense of the panel's scientific credibility and pointed criticism of agency leadership.

Kennedy, a longtime anti-vaccine activist, fired all 17 members of the committee after President Donald Trump named him as the nation's top health official this year, and created a panel with 12 people, many of whom have advocated against vaccine use. Kennedy has also scaled back recommendations on who should get the COVID-19 shot.

The committee will vote on removing recommendations to use the combined measles-mumps-rubella-varicella vaccine in children under age 4. It also is planning to vote on dropping a recommendation that all babies be vaccinated against hepatitis B at birth.

Kulldorff is a biostatistician and epidemiologist who publicly criticized lockdowns pursued during the COVID-19 pandemic aimed at limiting the spread of the disease. He was fired by Harvard for refusing to take a COVID-19 vaccine.

CDC head Susan Monarez was fired last month after clashing with Kennedy over vaccine policy, saying she was asked to rubber-stamp recommendations. Several senior CDC officials quit, citing concerns that policy decisions were being made without scientific review.

Kulldorff said he had never been contacted by Monarez, and challenged nine former CDC directors to debate him publicly, dismissing their accusations that the revamped committee was "unqualified" or held "dangerous" views.

He also said the panel was not anti-vaccine but pro-vaccine, defending its decision at its last meeting to stop distributing flu shots that contain the long-used mercury-based preservative thimerosal, calling it a known toxin. Decades of study have shown no related safety issues.

On Wednesday, Monarez testified to a Senate committee that Kennedy had told her in August that the U.S. vaccine schedule would change in September. The CDC director has had the authority to approve or deny recommendations from the panel in past years.

SHOTS UNDER REVIEW

The change to the combined MMWR shot recommendation is based on studies that show it has been linked to a higher risk of seizures in children under 4 years old than those who received separate measles-mumps-rubella and varicella shots.

The CDC already recommends that separate MMR and varicella vaccines be given under age 4 unless parents express a preference for the combined shot.

The committee will also vote on whether the hepatitis B vaccine should continue to be given to all newborns at birth or be delayed until one month of age or through shared clinical decision-making with the mother, unless the mother tests positive for the virus.

In addition, it will vote on whether all pregnant women should be tested for hepatitis B, a viral disease that can lead to liver cancer, cirrhosis or death. Many doctors have said that it is a key vaccine for babies, and U.S. government data shows that after newborn shots went into place in 1991, there was an 80% reduction in annual deaths by 2000.

"The U.S. didn't make much progress in combating hepatitis B until they moved to the birth dose," said Noel Brewer, one of the fired committee members. "They had tried risk-based vaccination, and it didn't really work very well. ... People who are high risk rarely think of themselves that way."

(Reporting by Michael Erman, additional reporting by Sriparna Roy, Mrinalika Roy in Bengaluru; Editing by Caroline Humer, Lisa Shumaker, Will Dunham and Chizu Nomiyama)