A CDC advisory panel is weighing a major change to the long-standing recommendation that all newborns receive a hepatitis B vaccine within 24 hours of birth.
Under the proposal discussed Thursday, only infants born to mothers who test positive for the virus would still get the shot at birth, while other babies would wait until their two-month visit.
The debate grew tense after last-minute wording changes forced the committee to delay a vote, which is now expected Friday.
The birth-dose has been standard since the early 1990s and is credited with sharply reducing childhood hepatitis B infections.
Public-health experts warn that rolling it back could leave newborns vulnerable, especially when maternal screening is missed or incomplete.
Supporters of the change say universal birth-dosing is unnecessary and that most infants can safely begin the series later.
The final vote will determine whether the U.S. shifts away from one of its oldest routine vaccine recommendations.