From WebMD:
it's not clear that US physicians who are not government officials have any legal obligation ― as opposed to a moral obligation ― to the government or the public to promote public health, said Jonathan Moreno, PhD, a professor of medical ethics at University of Pennsylvania, Philadelphia, Pennsylvania. "Is transmitting misinformation about COVID-19 public health malpractice?" he asked. "Do we as a society see physicians having a special role as guides in an emergency? I'd like to think we do, but we don't have a strong tradition like that in the US."