Vaccines are now on their way to parts of the world where vaccines are sorely lacking. The Biden administration is exporting an initial batch of 25 million doses from a promised 80 million for countries in need, part of the president's pledge on June 3 to "lead the world in the fight to defeat COVID-19."The private sector is jumping in as well. On Tuesday, the Mastercard Foundation announced a $1.3 billion donation over the next three years to assist the Africa Centres for Disease Control and Prevention in vaccinating at least 50 million people on the continent. But is it enough to beat back a virus that has already killed more than 3.7 million people globally and continues to mutate in alarming ways?The Biden donations are designated for a wide range of countries in Latin America, the Caribbean and parts of Asia and Africa. The remaining 55 million should arrive by the end of June, says White House COVID-19 Response Coordinator Jeff Zients. It's a welcome albeit belated sign of shifting U.S. priorities. Foreign leaders and health experts say the 80 million doses must be swiftly followed with substantially more vaccines and assistance. "It's a good start, but we could be contributing a lot more," says Dr. Denise Garrett, vice president of Applied Epidemiology at the Sabin Vaccine Institute. "We have a lot of vaccines that are sitting somewhere in a warehouse, and they need to be in people's arms," she says. The U.S. alone has purchased about 1.1 billion doses of COVID-19 vaccines from manufacturers and, with a total population of 328 million, will have hundreds of millions of excess doses. Meanwhile, about 2 billion shots have been administered worldwide — more than 80% in either high income or upper middle income countries. "This 80 million is about priming the pump for much more supply that needs to come in to make a meaningful impact over the next weeks to months," says Dr. Krishna Udayakumar, director of the Duke Global Health Innovation Center. The U.S could have 300 million excess dosesby the end of July and the European Union and G7 countries could have anywhere from 1 to 2 billion excess doses available in 2021, according to two analyses by Udayakumar and his colleagues. "Timing is really critical here. Doses in December or next year are going to be much less meaningful than sharing doses this summer," he says. COVAX — the global vaccination initiative co-led by the World Health Organization (WHO) — is distributing 75% of the doses from the U.S., although White House officials say they will ultimately decide which countries receive them. As the world's largest vaccine distributor, COVAX set out to ensure that 20% of the world's population was vaccinated by the end of the year but has struggled to secure enough shots to stay on track. "COVAX has been sort of an underperformer," says Dr. Ingrid Katz,associate faculty director of the Harvard Global Health Institute. "It has the potential to be a very important piece at this moment, but it hasn't lived up to that as of yet." In fact, COVAX faces a shortfall of 100 million doses in June and July and will need another 250 million doses by September — in part because India, where the majority of vaccines are manufactured, has diverted those doses for its own population in response to the country's horrific surge in infections. Last week, nearly 40 countries committed about$2.4 billion to fund the COVAX program, which will help pay for about 1.8 billion doses and eventually cover 30% of the adult population in lower income countries. Despite the burst of global generosity, many countries are still desperate for more shots. This week, WHO Director-General Tedros Adhanom Ghebreyesus called on nations in the G7, slated to meet in the U.K. later this week for the annual summit, to commit to share hundreds of millions of doses in June and July."COVAX is the best way to distribute vaccines quickly and equitably," Tedros told reporters, "sharing vaccines now is essential for ending the acute phase of the pandemic."The initial allotment of 80 million doses represents just the "beginning" of America's contribution and part of a broader strategy to end the pandemic, which will also include helping countries deliver vaccines and curb the spread of the virus, said Gayle Smith, the U.S. State Department coordinator for Global COVID-19 Response and Health Security. "We're not doing this to curry any political favor," Smith told reporters on Friday. Meanwhile, there are many outstanding questions about the U.S. global plan. "We need a proper strategy — what are the goals going to be? What's going to happen in three months? In six months?" says Dr Junaid Nabi, a fellow at the Aspen Institute and senior researcher at Harvard Business School. Even the calculus behind how the U.S. is divvying up the doses is still somewhat murky. For example, the U.S. is not sending all of its doses to COVAX but is instead setting aside 25% to be used in a "flexible" way, sending the vaccine directly to regions with "immediate needs" like India and the West Bank and Gaza. "We really need to be able to see what the rationale is behind these kinds of decisions because the person you didn't give to is going to be mad," says Amanda Glassman, chief executive officer at the Center for Global Development."Many of these countries have purchased enough vaccines to cover 60% or more of their populations, but the issue is the delivery date because they're at different places in the line." Udayakumar says the U.S. needs to go beyond the current framework used by COVAX — one based purely on population vaccine coverage — and factor in where the doses will have the greatest impact, like in India and Brazil."We should be using some clear and transparent criteria, including where we can avert the most deaths and suffering, where the health systems are most fragile or at risk of collapsing, and where we can stop transmission, especially of variants of concern," he says. And Dr. Nabi says the focus on giving away doses in a piecemeal fashion — what can have connotations of "charity" — also misses other key ways the U.S. can support the global vaccination campaign. This includes helping "countries develop capacity to produce the raw materials" and "transfer technology," so local manufacturers can produce vaccines. "That would go a long way so countries don't have to constantly depend on, 'OK, we received 20 million this month, but are we going to receive 20 million the next month?' "Some countries that ordered vaccines are stuck waiting for their deliveries from COVAX. Others have the vaccines only to run into problems getting them into peoples' arms. Malawi ended updestroying thousandsof vaccines because they had expired. The Democratic Republic of Congo returned more than 1 million doses after realizing it would not be able to use them before their expiration date."That's what's going to start happening everywhere unless we are thinking of doses and delivery at the same time," says Ritu Sharma, vice president for U.S. programs and policy at CARE USA. Sharma's organization estimates that globally for every one dollar spent on actual vaccines, five dollars needs to be invested in getting those vaccines to the people who need them. "That means transportation. That means the community health workers who will need training to give those shots. That means education for community members so that they are willing to get vaccinated," she says. Copyright 2021 NPR. To see more, visit https://www.npr.org.