A Department of Health and Human Services spokesperson called the move "a radical departure from past practices."

The top US health department plans to require placebo testing for all vaccines in an effort to offer "straightforward" public health information, but experts say such testing could limit availability and raise ethical concerns.

Kennedy Jr. intends to shift the way vaccines are tested, a move that the agency said will increase transparency but that medical experts fear could limit access to vaccines and undermine the public’s trust in immunization depending on its implementation.