The Trump administration plans to impose a new testing requirement for new vaccines — a demand that could delay the availability of the next round of COVID-19 vaccines and complicate the approval of other vaccines.

The administration will require all new vaccines to be tested against an inert substance known as a placebo before they can be made available, which is a "radical departure from past practices," according to a statement from Andrew Nixon, a spokesman for Robert F. Kennedy Jr., the secretary of Health and Human Services.

The latest statement triggered alarm among vaccine experts that this may be another step by Kennedy to undermine the confidence in and availability of vaccines.