The US Department of Health and Human Services said it will require that all new vaccines be tested in placebo-controlled trials before they’re licensed for use, raising urgent questions about the system used to clear updated Covid-19 boosters each respiratory virus season.

The potential change outlined in a statement would require all new vaccines to undergo placebo testing, sparking concerns among medical experts.

U.S. Health and Human Services Secretary Robert F. Kennedy Jr intends to shift the way vaccines are tested, The Washington Post reported on Wednesday, citing a spokesperson from the HHS.