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/Jonathan Ernst/File Photo

(Reuters) - U.S. vaccine advisers will reconvene on Friday for the second session of a key meeting to decide on hepatitis B and COVID-19 shots, after a tense opening day that highlighted divisions over the future of the country's immunization schedule.

The group, which advises the Centers for Disease Control and Prevention on U.S. vaccination schedules, had been expected to vote Thursday on whether babies born to mothers who test negative for hepatitis B should receive their first dose at one month of age instead of within 24 hours of birth.

The vote was pushed to Friday due to a "slight discrepancy" in voting language. The panel will also decide on updates to COVID-19 vaccine guidance.

On Thursday, the advisers recommended against use of the combined measles-mumps-rubella-varicella vaccine for children under age four, citing a slight increase in febrile seizure risk.

Instead, separate vaccine shots will be given for measles-mumps-rubella and varicella.

The votes were the first from the 12-member Advisory Committee on Immunization Practices (ACIP), reconstituted by U.S. Health Secretary Robert F Kennedy Jr., many of whom have advocated against vaccine use.

Kennedy has long promoted the view, contrary to scientific evidence, that many vaccines routinely administered to children cause grave harm.

CDC staff presenting to the panel on Thursday stressed that the hepatitis B vaccine at birth remains a critical safeguard, noting that 12% to 16% of pregnant women in the U.S. have no record of hepatitis B testing.

Pediatrician Dr. Cody Meissner, a member of the ACIP panel, warned delaying the first dose of the hepatitis B vaccine could do more harm than good.

"If we change the recommendation for neonatal administration, we will increase the risk of harm based on no evidence of benefit," he said during Thursday's meeting.

Experts have also warned that infants are uniquely vulnerable if left unprotected.

"I am not sure what would be gained by delaying it by one month," said Dr. Catherine Troisi, infectious disease epidemiologist at UTHealth Houston, crediting the birth-dose policy with driving a 97% decline in acute hepatitis B among Americans under 19.

Under Kennedy's leadership, the Department of Health and Human Services has made several sweeping changes to the COVID vaccine policy.

The agency dropped routine shots for children and pregnant women, focusing instead on older and high-risk groups. Kennedy has also halted nearly $500 million in mRNA projects.

(Reporting by Mrinalika Roy in Bengaluru; Editing by Sriraj Kalluvila)