NEW YORK (AP) — U.S. health officials Wednesday announced plans to dispense 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.

Health officials said people who received the single-dose Johnson & Johnson vaccine will also probably need extra shots. But they said they are awaiting more data and have yet to work out the details.

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

In a statement, health 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.

Top scientists at the World Health Organization bitterly objected to the U.S. plan, noting that poor countries are not getting enough vaccine for their initial rounds of shots.

“We're planning to hand out extra life jackets to people who already have life jackets, while we're leaving other people to drown without a single life jacket,” said Dr. Michael Ryan, the WHO's emergencies chief.

The organization's top scientist, Dr. Soumya Swaminathan, said: “We believe clearly that the data does not indicate that boosters are needed” for everyone. She warned that leaving billions of people in the developing world unvaccinated could foster the emergence of new variants and result in “even more dire situations.”

WHO officials have repeatedly expressed concerns that variants will continue to crop up in areas where the virus goes unchecked through measures like vaccination. They have called for vaccine equity and “solidarity” among countries.

But White House press secretary Jen Psaki this week said the question of whether to distribute boosters or help other nations “is a false choice. We can do both.”

She said the U.S. is “far and away” the biggest contributor to the global fight against COVID-19 and will “continue to be the arsenal for vaccines” to the world. She added that the U.S. has enough vaccine for dispense boosters to the American people.

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