More than 50 percent of the adult population in the U.S. has been fully vaccinated against COVID-19. But the situation is very different in much of the rest of the world. In many low-income nations, less than 1 percent of the population has received a single dose.

Addressing this inequity is the mission of COVAX, a collaboration among Gavi, the Vaccine Alliance, the Coalition for Epidemic Preparedness Innovations and the World Health Organization (WHO). COVAX launched in April 2020 with the aim of distributing two billion vaccine doses by the end of 2021. The idea was to accept donations of money and vaccines from countries and allocate them equally to poorer nations based on their population.

But so far, COVAX has fallen short of its aims. The collaboration has accounted for only 4 percent of more than two billion shots administered worldwide to date, largely because wealthy countries bought most of the new vaccines before they were even approved by regulators for emergency use.

Another major setback came earlier this year, when India suspended the export of vaccines made in the country, which has been suffering a devastating outbreak. COVAX had been relying on the Serum Institute of India to supply more than half of its doses, and the resulting shortage left the organization unable to fulfill its pledges to many countries. In a statement to Scientific American, a Gavi spokesperson said that the organization now expects to deliver 1.8 billion vaccines by end of the first quarter of 2022.

The situation may be turning around. On June 3 President Joe Biden announced that the U.S. will share 19 million doses with COVAX by the end of the month and directly provide another six million to countries in need. At the recent G7 summit in England, wealthy nations pledged a total of 870 million vaccines to COVAX, and half of them should arrive by the end of the year.

Even if COVAX were to achieve its goal perfectly, it would only vaccinate 20 percent of participating countries’ populations. That figure is far less than the proportion epidemiologists predict is necessary to achieve herd immunity, the point at which the novel coronavirus is unlikely to spread within a population. Experts say that other efforts will be needed, especially when it comes to administering vaccines in remote regions, dealing with vaccine hesitancy and expanding the number of facilities that can manufacture vaccines. “I’d characterize COVAX as necessary but not sufficient,” says Krishna Udayakumar, director of the Duke Global Health Innovation Center. Until wealthy countries and companies step up efforts to share vaccines and help distribute them worldwide, the collaboration’s hands are tied, he says. “Unfortunately, as usual, low-income countries continue to be at back of the line or at the mercy of high-income countries,” Udayakumar adds.

One of the complications was the speed at which COVAX began purchasing doses, says Alain Alsalhani, a vaccines pharmacist at the Médecins Sans Frontières/Doctors without Borders Access Campaign. Although Gavi routinely delivers other vaccines to many low-income countries, the organization had to strike new agreements with other nations and figure out how many COVID vaccines it would need before it could approach the pharmaceutical companies. By the time it got in the game, wealthy countries had bought most of the yet-to-be-made doses. “You can’t claim to be a global supply mechanism if you represent 4 percent of the supply in the world,” Alsalhani says.

Gavi says that the delay was a question of funding. “COVAX started making deals with manufacturers as soon as money started arriving from participants and donors. Had money been available earlier, doses could have been locked in earlier,” said a Gavi spokesperson in a statement to Scientific American, adding that it is impossible to compare COVID vaccine rollout with the routine vaccinations it provides. “The challenge of ensuring access to vaccines during a pandemic is different to any other time, because the vaccine is needed everywhere at a similar point in time. All countries are affected, and therefore questions of manufacturing and overall supply are vastly more complex.”

In addition to waiting for COVAX, many low- and middle-income countries have struck their own deals directly with companies and other nations. It can be a risky strategy: some critics have accused countries such as China of engaging in “vaccine diplomacy” by donating its Sinovac and Sinopharm vaccines, for example, in exchange for political influence in a region, Udayakumar says. But impoverished countries that cannot buy their own vaccines may have little choice other than to accept these donations.

A further concern is that such deals could lead to poorer nations primarily getting less effective vaccines, Udayakumar says. While no one has yet directly compared China’s vaccines with those developed in the U.S. and Europe, experts estimate that they offer less protection than mRNA vaccines such as those made by Pfizer and Moderna, which are less widely available to developing countries. “If we’re not careful, that’s unfortunately the direction we’re heading in,” he says.

Alsalhani adds that the concerns about blood clots linked to certain vaccines have lowered the demand for them around the world. In many low-income countries, people would prefer the Pfizer and Moderna mRNA vaccines that wealthy countries are receiving. “Even if the U.S. and Europe start sharing AstraZeneca [and Johnson & Johnson vaccines], I’m not sure this is going to be very helpful,” he says.

The difference between vaccine types has become a flashpoint in the Democratic Republic of the Congo (D.R.C.), whose government sat on 1.7 million doses of AstraZeneca’s vaccine while the company investigated reports of blood clots. By the time European regulators cleared the vaccine, which had been acquired through COVAX, the D.R.C.’s doses were about to expire, and COVAX redistributed 75 percent of them to other African countries. Now lingering concerns about the AstraZeneca vaccine’s side effects, along with widespread rumors and skepticism about the existence of COVID itself, have led to low demand for vaccines among the Congolese public, says Freddy Nkosi, D.R.C. country director at the nonprofit VillageReach. As of June 14, less than 1 percent of the nation’s population has received one dose.

Even if developing countries could get access to highly effective mRNA vaccines, another problem is keeping them cold while transporting them to remote regions of the D.R.C.—the 11th largest country in the world by land area—and the lack of health infrastructure and workers to administer doses. “Although there was a huge investment made to get [vaccines] into the country, there was not much investment in terms of delivery to communities,” Nkosi says. “There was very little investment to raise community awareness around the new vaccine.” He hopes that the increasing number of people, including African celebrities, who have received a COVID vaccine will help engender trust among the public.

On the other side of the world, delivery problems have also plagued Peru, which has had the highest reported per capita COVID death rate of any country in the world. Political upheavals further slowed vaccine rollout in the country, which held a highly contested runoff election for its fifth president in five years on June 6. In addition to the challenge of delivering vaccines to people in Peru’s rural highlands and jungles, that leadership turmoil has resulted in less than 6 percent of the country being fully vaccinated, says Ricardo Díaz Romero, head of community health at the nonprofit CARE Peru.

A political scandal further derailed vaccination efforts: Peruvian politicians jumped the line to receive Sinopharm vaccines intended for a clinical trial. When the story came to light, rumors spread that regulators had approved that vaccine for political reasons instead of efficacy. “People lost their trust,” says Valerie Paz-Soldán, a Lima, Peru–based social scientist at Tulane University. The country has also been slow to buy and import vaccines, including 38 million Sinopharm vaccines from China that it secured in January. Now Peru has signed additional agreements with AstraZeneca, Pfizer and COVAX, but Paz-Soldán says actual shipments are trickling in at the rate of a few hundred thousand at a time.

Ultimately, vaccinating the world will require more help from wealthy countries and companies. In May the Biden administration announced it supported waiving patents on COVID vaccines. But vaccinating the world will require not just vaccines but know-how, says Richard Marlink, director of the Rutgers Global Health Institute. Expanding the number of facilities that can manufacture vaccines and training workers, for instance, could help resolve bottlenecks and make it easier for regions such as Africa and Southeast Asia to acquire vaccines quickly. And increasing funding for the WHO and other agencies could help build the infrastructure necessary not only to develop vaccines but also to distribute them globally. “I hope that what the pandemic is going to teach us is investing in public health is just as important as investing in individual health,” Marlink says.