Health Secretary Robert F. Kennedy Jr. announced a plan that would require placebo-controlled studies for all new vaccines, surprising some experts who noted that such testing already routinely took place.

In a statement, Andrew Nixon, a spokesman for the Department of Health and Human Services, said that “all new vaccines will undergo safety testing in placebo-controlled trials” before approval, and called the move a “radical departure” from existing standards.

Even though modern studies routinely use placebos,one exception has been the Covid booster shots, which have been authorized without human trials to target new strains of the virus as it has evolved. It’s unclear how the announcement will affect availability of Covid vaccines that were expected to be updated for the fall.

Mr. Kennedy also announced an effort Thursday for the National Institutes of Health to turbocharge the development of new inoculations for Covid, bird flu and seasonal flu.

The new vaccine development initiative would involve methods other than the mRNA technology used to develop the dominant Covid vaccines that are already in use, a statement from the Health and Human Services department said. The mRNA shots have been the subject of conspiracy theories, and Mr. Kennedy has intensely criticized them.

Taken together, the moves suggest that Mr. Kennedy will reach far into the details of vaccine development, an effort likely informed by his decades as one of the nation’s most vocal critics of immunization oversight.