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 takes place routinely.

In a statement, Andrew Nixon, a spokesperson 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.

Modern studies tend to use placebos. One exception has been the COVID-19 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-19 vaccines that were expected to be updated for the fall.

Kennedy also announced an effort Thursday for the National Institutes of Health to turbocharge the development of new inoculations for COVID-19, bird flu and seasonal flu.

The new vaccine development initiative would involve methods other than the mRNA technology used to develop the dominant COVID-19 vaccines that are in use, a statement from the Health and Human Services department said.

The mRNA shots have been the subject of conspiracy theories, and Kennedy has criticized them intensely.

Taken together, the moves suggest that 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.

Although some scientists say the quest to fully understand the possible unanticipated effects of vaccines is worthwhile, they also warn that doing so in a way that delays approval of lifesaving shots could jeopardize public health.

Kennedy’s activism in recent years included petitioning the Food and Drug Administration to pull the COVID-19 vaccine off the market in 2021, during a deadly phase of the pandemic. He also urged the FDA not to authorize COVID shots for children.

Asked about how the new testing policy would affect COVID booster shots, Nixon suggested that new trials could be requested. Although the vaccines authorized by the FDA initially were studied in large trials against placebos, Kennedy and others have criticized the lack of clinical trials for the boosters.

“As we’ve said before, trials from four years ago conducted in people without natural immunity no longer suffice,” Nixon said. “A 4-year-old trial is also not a blank check for new vaccines each year without clinical trial data, unlike the flu shot, which has been tried and tested for more than 80 years. The public deserves transparency and gold-standard science — especially with evolving products.”

Pfizer and Moderna, makers of the mRNA COVID-19 shots, did not respond immediately to requests for comment. The Washington Post first reported the policy shift.