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... 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.