Though Covid-19 vaccines authorized in the United States “continue to be remarkably effective in reducing the risk of severe disease,” the Biden administration has concluded a booster shot will be needed to maximize protection offered by the Pfizer and Moderna vaccines, health officials announced in a statement Wednesday. 

“Based on our latest assessment, the current protection against severe disease, hospitalization, and death could diminish in the months ahead,” the officials, led by Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, and Dr. Janet Woodcock, acting Commissioner for the Food and Drug Administration, said Wednesday. 

The plan is still subject to approval from the FDA and the CDC’s vaccine advisory committee, but officials say they are prepared to begin the rollout of booster shots starting the week of September 20.

In a press briefing, Jeff Zients, the White House’s coronavirus response coordinator, said boosters would be free to eligible Americans and available at 88,000 locations, with the administration aiming to give out 100 million doses by year’s end.

The decision comes after health officials in recent weeks have started cautioning about waning vaccine efficacy demonstrated by data from nations like Israel that started vaccinating their populations in large numbers before the U.S., and marks a major pivot from the Biden administration’s instance just two weeks ago that Americans did not yet need a booster. 

“​​We don’t want to wait until it’s too late, so that’s why we’re looking at the data,” Director of the National Institutes of Health Dr. Francis Collins, who also signed the Wednesday announcement, said Tuesday, noting that data in Israel shows people immunized in January “are the ones that are now having more breakthrough cases.”