National Institutes of Health Director Dr. Francis Collins called Israel’s data on Covid-19 booster shots “impressive,” noting that they provided a tenfold reduction in infection for people who received a third dose.

Israel began administering boosters in late July to individuals over 60, giving scientists more time to examine their ability to combat Covid and bolster the waning effectiveness of the initial series of doses. Collins’ comments Thursday came just a day after the Food and Drug Administration approved Pfizer and BioNTech’s Covid booster for high-risk people, including anyone 65 and older.

“Without tipping my hand too much, I will say the data looks really impressive, that the boosters do in fact provide substantial reduction in infection,” Collins said during a discussion on Covid hosted by Bloomberg Philanthropies. “Like a tenfold reduction just within 12 days after that booster, and also a reduction in severe illness, which is the thing we’re most concerned about.”

Collins added that the Israeli data indicated a roughly twelvefold reduction in severe Covid as the nation was starting to experience more breakthrough cases. Pfizer reported on Aug. 25 that recipients of its third doses experienced a threefold increase in antibodies.

The CDC’s Advisory Committee on Immunization Practices, a panel of medical authorities who offer guidance to the agency, will vote Thursday on whether to endorse the FDA’s booster decision. The panel began a two-day series of presentations on boosters on Wednesday to give experts and the public a chance to hear more data before the final vote.