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.

Public health experts warn that the change could lead to people getting a placebo shot instead of a necessary vaccine.

Health and Human Services Secretary Robert F. Kennedy Jr. Is changing the way vaccines are tested and will now require all new vaccines to undergo safety testing in placebo-controlled trials,