US President-elect Donald Trump has appointed a vaccine sceptic, Robert F Kennedy, a son of the late US Senator Robert F. Kennedy, to chair a commission on vaccine safety and scientific integrity.
The appointment is likely to reignite debate over now-debunked research that tied childhood immunizations to autism.
"President-elect Trump has some doubts about the current vaccine policy, and he has questions about it," Mr Kennedy, who has raised questions about the safety of vaccines, told reporters following a meeting with Mr Trump in New York on Tuesday.
"He asked me to chair a commission on vaccine safety and scientific integrity. I said I would."
Vaccine experts decried the appointment of a vocal vaccine sceptic to explore the safety of vaccines and their purported link with autism, an association raised by a paper published in The Lancet in 1998 that claimed to find a connection between the measles, mumps and rubella (MMR) vaccine and autism.
That paper has been debunked, and The Lancet withdrew the study. Since then, numerous studies have affirmed the safety of the vaccine, most recently including a study of 100,000 children considered at high risk of developing autism.
"The concerns of public health officials and paediatricians and family doctors regarding the Trump administration and its attitude toward vaccines have just been reinforced," said William Schaffner an infectious disease expert at Vanderbilt University School of Medicine, who advises the federal panel that sets US vaccine policy.
Dr Schaffner said Mr Kennedy had "raised issues that have been settled securely and completely by good science, and 80,0000 paediatricians, many family doctors and the World Health Organization all reinforce the current recommended childhood immunization schedule. They are safe and they are effective."
Nevertheless, concerns have persisted over a possible link between vaccines and autism spectrum disorder, a range of symptoms that often includes difficulties with communication and social interaction.
"Everybody ought to be able to be assured that the vaccines that we have - he's very pro-vaccine, as am I - but they're as safe as they possibly can be," added Mr Kennedy.
Daniel Johnson, an expert in paediatric infectious disease at University of Chicago Medicine, said he thought yet another investigation into vaccine safety was a waste of public money.
"There's already many systems in place to provide oversight, to record data, which is constantly being reviewed by many in government and the scientific community. There is no need for still yet another system for doing this," Dr Johnson said.
He said he was "very concerned" that parents may delay getting their children vaccinated as they await the outcome of this panel, which could result in "increased harm, illness and potentially death" of children from diseases that could be prevented by vaccines.