Dr. Anthony Fauci has shared that Moderna’s COVID-19 vaccine booster doses could be delayed from their expected roll out on the week of Sept. 20, while Pfizer’s booster appears on track for approval

Speaking with CNN’s Jim Acosta, Joe Biden’s chief medical adviser revealed that the administration’s plan to share both Pfizer and Moderna booster doses simultaneously may not happen, and that “things look like they’re ready to go” for Pfizer, which has submitted information to the U.S. Food and Drug Administration as it seeks approval.

“I don’t think that is a major issue there, but we would have liked to have seen it happen all together, simultaneously. But ultimately the plan will be implemented, as was put forth,” Fauci said, revealing that Moderna could roll out a week or two later. 

In order for the boosters to roll out, both companies must send specific data to the FDA, get approved, and then be recommended by the Centers for Disease Control and Prevention vaccine advisers, per CNN. 

“What we’re observing now – not only here in the United States but in other countries, including Israel and the UK – [is] that the durability of the protection tends to wane, particularly in the context of the Delta variant,” Fauci said, adding that three doses may be the best regimen for protecting against COVID. 

He explained that Israel, who’s a “month or so” ahead of the U.S., showed a “substantial diminution in protection against infection and an unquestionable diminution in the protection against hospitalization,” judging by booster-related data. 

“Importantly, their data also show that when you give those boosters you reconstitute, to an even higher level than before, the protection against both infection and hospitalization,” Fauci said. “The boosters really jack up the response very, very high, and we hope that that response would be durable.”