The nation’s leading doctors groups are in a standoff with federal health officials over vaccines. The conflict intensified when an advisory panel, handpicked by Health Secretary Robert F. Kennedy Jr., a longtime anti-vaccine activist, recommended ending routine hepatitis B vaccinations for newborns without presenting new evidence. This vaccine, which has drastically reduced the liver disease and liver cancer, continues to be recommended by the American Academy of Pediatrics and other medical groups. Doctors are concerned about mixed messages eroding public trust. They urge parents to consult their doctors for guidance.