SEOUL, South Korea (AP) — Health officials and experts in Asia have welcomed U.S. plans to share 500 million more doses of the Pfizer vaccine with the developing world, but some say it would take more than donations alone to address huge vaccination gaps that threaten to prolong the pandemic.

President Joe Biden was set to make the announcement Thursday in a speech before the start of the Group of Seven summit in Britain. Two hundred million doses — enough to fully protect 100 million people — will be provided this year, with the balance donated in the first half of 2022, according to the White House.

Jaehun Jung, a professor of preventive medicine at South Korea’s Gachon University College of Medicine, said the U.S. donations may prove to be a “huge turning point” in the global fight against COVID-19, but also lamented that the help didn't come earlier.

He said the extremely cold storage temperatures required for Pfizer shots would also present challenges for countries with poor health systems and infrastructure and called on U.S. officials and the drugmaker to help those nations overcome these challenges. Partially because of these concerns, many of the vaccines currently being used in the developing world are shots that have simpler storage requirements, such as AstraZeneca's.

As richer countries have rushed to vaccinate wide swath of their populations, inequities in vaccine supplies around the world have become more pronounced — with some poorer nations yet to administer a single dose. At the same time, there’s increasing concern over newer virus variants emerging from areas with consistently high COVID-19 circulation.

The U.S. and some other developed countries have faced increasing pressure to do more. Jung said the delay in U.S. help was “understandable ... but for now, it’s critical to move up the timing of the vaccine provisions to the earliest possible point.”

The Biden administration plans to provide the 500 million shots it purchases from Pfizer to 92 lower income countries and the African Union over the next year through the U.N.-backed COVAX program — which was designed to get doses to poorer countries but has struggled to do so. The drugmaker 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 plans to share 80 million doses globally by the end of June, most through COVAX.

The additional 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, the head of the International Vaccine Institute, a nonprofit dedicated to making vaccines available to developing countries.

Jeong Eun-kyeong, director of South Korea’s Disease Control and Prevention Agency, said the success of Biden’s vaccine-sharing plan would depend mainly on how fast the shots could be manufactured and sent to countries in need amid global shortages. The White House has said all the doses will be manufactured in the U.S.

Jeong also echoed concerns about Pfizer’s cold-chain requirements and said the U.S. donations should be accompanied by efforts to improve infrastructure and educate health workers in receiving countries.

“It’s very important to manage international cooperation so that the whole world can be vaccinated quickly,” she said during a briefing.

In Asia, Jung said that India and Southeast Asia are in desperate need of donations. Vaccinating isolated North Korea could also prove to be a difficult challenge.

Perhaps reflecting that many of the details of the donation plan are not yet clear, Indonesia’s spokesperson for its COVID-19 vaccination program said the country would take a wait-and-see approach.

“We will wait from COVAX. If there are new vaccines, COVAX will offer and distribute to the countries,” Siti Nadia Tarmizi said.

Some experts said donations alone wouldn't 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. and some other world leaders have backed suspending IP protections on vaccines — but Jung noted that many developing countries don't have the capacity to manufacture advanced vaccines like Pfizer's mRNA shots and so wouldn't be able to take advantage of such measures.

As countries around the world struggled to access vaccines, unable to secure bilateral deals with companies like Pfizer, many have turned to China. China has exported 350 million doses of its vaccines to dozens of countries, according to its Foreign Ministry.

China has pledged 10 million doses to COVAX, and the Chinese drug maker Sinopharm said last week it had just finished a batch of vaccines for sharing with COVAX. The World Health Organization had approved the vaccine for emergency use last month.

While Chinese vaccines have faced scrutiny because of a lack of transparency in sharing clinical trial data, many countries were desperate to take what was available and found the shots easier to use as they could be stored in normal refrigerators.

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Wu reported from Taipei, Taiwan. Associated Press writer Edna Tarigan in Jakarta, Indonesia, contributed.