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.

The new policy, revealed by the Department of Health and Human Services on Wednesday, would make vaccines “less available and less affordable,” according to vaccine expert Paul Offit. It could also further complicate the picture for companies like Novavax.