If the FDA deems Pfizer’s and Moderna’s updated vaccines “new” products, it’s extremely unlikely the doses would be ready for the fall, vaccine experts say.

New rules implemented by Health and Human Services Secretary Robert F. Kennedy Jr. will require updated existing vaccines to undergo the same testing as completely new vaccines, which could add months of delay to production.

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.