NEW YORK (AP) — U.S. health officials Wednesday announced plans to offer COVID-19 booster shots to all Americans to shore up their protection amid the surging delta variant and evidence that the vaccines’ effectiveness is falling.

The plan, as outlined by the director of the Centers for Disease Control and Prevention and other top authorities, calls for an extra dose eight months after people get their second shot of the Pfizer or Moderna vaccine. The doses could begin the week of Sept. 20.

“Our plan is to protect the American people, to stay ahead of this virus,” CDC Director Dr. Rochelle Walensky said in a statement.

Health officials said people who received the single-dose Johnson & Johnson vaccine will also probably need extra shots. But they said they are waiting for more data.

The overall plan is subject to a Food and Drug Administration evaluation of the safety and effectiveness of a third dose, the officials said.

In a statement, officials said it is “very clear” that the vaccines’ protection against infection wanes over time, and now, with the highly contagious delta variant spreading rapidly, “we are starting to see evidence of reduced protection against mild and moderate disease.”

“Based on our latest assessment, the current protection against severe disease, hospitalization and death could diminish in the months ahead,” they said.

Dr. Mark Mulligan of NYU’s Langone Health center welcomed the announcement as a “proactive” response to signs that vaccine strength is eroding.

“There are hints that this may become an increasing problem given waning immunity mixed with the delta variant,” he said. “Part of leadership is being able to see around the corner and make hard decisions without having all the data. It seems to me that’s what they’re doing here.”

By — Nick Ursini