CAPE TOWN, South Africa (AP) — U.S. plans to donate 500 million more COVID-19 vaccines to developing countries were met Thursday with both celebration and hesitation amid questions over whether the effort will be enough to help poor regions desperate for doses.

Some health officials and experts expressed hope that the pledge would encourage more donations to ease the inequities in vaccine supplies that have become pronounced in recent months. Inoculation campaigns in several richer countries have surged ahead while efforts have barely begun in many poorer nations. Other observers stressed that the doses needed to roll out quickly.

The first 200 million doses will start to arrive in countries in August, the White House and manufacturer Pfizer said, with the rest following in the first half of 2022.

“Saving lives requires shots in arms now. Not at the end of 2021, not in 2022, but now,” said Kate Elder, senior vaccines policy advisor to the Doctors Without Borders organization. The donated vaccines “better come in sufficient volumes and urgently.”

The recent surge in cases in India was a searing reminder of how COVID-19 can still devastate entire countries.

“We’ve seen that the virus is not over. It might feel like it’s nearly over for some of us living in countries where we’re lucky enough to have been vaccinated. But in other parts of the world, the virus is still absolutely raging out of control," said Lily Caprani, head of vaccine advocacy for UNICEF.

The Biden administration’s decision to donate Pfizer vaccines raised doubts about whether the doses would reach the poorest of the poor because those doses need to be stored in ultra-cold conditions. Many low-income countries with limited infrastructure will probably be unable to take them to their most remote areas.

The Africa Centers for Disease Control and Prevention said it would advise its countries to use the Pfizer shots in major cities.

Still, the administration's promise was “clearly a cause for celebration,” said Dr. John Nkengasong, director of the Africa CDC, particularly at a time when infections are increasing on the continent of 1.3 billion people, and some countries still have not administered a single dose.

“Absolutely, it's going to be a big help,” Nkengasong said.

The donation of the Pfizer shots is crucial because the global disparity in vaccination has become a multidimensional threat: a human catastrophe, a $5 trillion economic loss for advanced economies and a contributor to the generation of mutant viruses, said Jerome Kim, head of the International Vaccine Institute, a nonprofit dedicated to making vaccines available to developing countries.

The U.S. will work with the global COVAX vaccine alliance to deliver the shots. U.S. President Joe Biden was expected to talk about the plan later Thursday in a speech on the eve of the summit of the wealthy Group of Seven democracies in Britain.

The summit might also give a crucial indication of whether and how far other nations in the elite club are willing to follow the U.S on vaccine sharing. Richer countries have been the focus of widespread criticism that they have fallen woefully short of lofty promises of fairness when the vaccines were being developed.

The gaps in vaccine access are clear: The U.S. and Britain have fully vaccinated more than 40% of their populations, according to a global tracker kept by Johns Hopkins University. Countries like Haiti, on America's doorstep, Burundi and many others have vaccinated few, if any, of their people.

“So far, 77% of all the vaccines administered have gone into the arms of people in 10 countries,” said COVAX Co-Chair Jane Halton. “Now that has got to change.”

The inequality is not just a matter of fairness. There is also increasing concern over virus variants emerging from areas with consistently high COVID-19 circulation. At least three variants are circulating in Africa, the African CDC said, and driving infections. Even countries like Britain, with high rates of vaccination, have cited variants as an ongoing concern.

British Prime Minister Boris Johnson wrote in The Times of London newspaper that it was now time for wealthy countries to “shoulder their responsibilities" and "vaccinate the world,” although his own country has yet to send any doses abroad or announce any solid plan to share vaccines. Johnson indicated Britain had millions of doses in surplus stocks.

Germany and France have each promised to donate 30 million doses by the end of the year.

“While Biden’s plan is welcome, it is a small piece of the puzzle, and it doesn’t help countries that are struggling now,” said Fifa Rahman, who is a civil society representative on a World Health Organization body focused on increasing access to COVID-19 vaccines.

She cited the East African nation of Uganda as an example, saying the country’s intensive care units are already full, and it has only small numbers of vaccines left.

Biden's announcement is also tangled up in geopolitics. He hopes to put the U.S. and its allies at the forefront of the global virus fight in the face of a growing supply of Chinese and Russian vaccines.

China has exported 350 million doses of its vaccines to dozens of nations, according to its Foreign Ministry. While those vaccines have faced scrutiny because of a lack of transparency in the sharing of clinical trial data, many poorer nations were eager to receive anything at all.

The shots promised by the Biden administration will go to 92 lower income countries and the African Union. Pfizer said the doses are part of a previous pledge, with its partner BioNTech, to provide 2 billion doses to developing countries over the next 18 months.

The White House had earlier announced separate plans to share 80 million doses globally by the end of June, most through COVAX.

Some experts said donations alone would not be enough to close the huge gaps in supplies and called for allowing qualified companies around the world to manufacture vaccines without intellectual property constraints.

The U.S. has expressed support for suspending IP protections on vaccines, and some other countries have agreed it should be explored. But in an indication of the disjointed response from the wealthy G-7 nations, Germany on Thursday repeated its opposition to such a waiver.

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Kim reported from Seoul, South Korea. Associated Press writers Huizhong Wu in Taipei, Taiwan; Edna Tarigan in Jakarta, Indonesia; Ken Moritsugu in Beijing; Maria Cheng in London; Jill Lawless in Falmouth, England; Angela Charlton in Paris; Geir Moulson in Berlin; and Rod McGuirk in Canberra, Australia, contributed.