With rich countries paying more for vaccines, the supply for Latin America is falling short, the W.H.O. says.

The U.N.-backed vaccine program will fail to meet its target for delivering doses to Latin America and the Caribbean this year, in part because wealthy countries that pay more for the shots are buying up most of the supply, a World Health Organization official said Wednesday.

The global Covax program, the primary source of Covid vaccines for most of the world, aimed to provide enough doses this year for Latin American and Caribbean countries to inoculate 20 percent of their people. But most countries have only received around 30 percent of the supply they contracted through Covax, said Dr. Jarbas Barbosa, assistant director of the Pan American Health Organization, a division of the W.H.O.

“Producers are not prioritizing delivery to the Covax mechanism,” Dr. Barbosa said at a news conference. “They continue to prioritize the bilateral agreements they have because in these bilateral agreements the vaccines are more expensive.”

Wealthy countries have raced far ahead of the rest of the world in vaccination rates, and continue to buy doses as demand for booster shots rises. The W.H.O. said last week that only nine of Africa’s 54 countries had met the goal of vaccinating 10 percent of their people by the end of September.

India’s prohibition on exporting vaccines has contributed to delays in delivering shots to other parts of the world. India, the world’s largest drug producer, imposed the ban in May as it fell behind on domestic vaccination, but it said recently that with production expanding and its own inoculation program gaining speed, it would lift the embargo this month.

Covax is focusing on delivery of vaccines to countries that have so far vaccinated less than 10 percent of their population. In the Americas, that includes, Jamaica, Nicaragua and Haiti.

With the Covax program faltering, the Pan American Health Organization has struck separate deals to buy millions of vaccine doses from China’s Sinopharm and Sinovac, as well as AstraZeneca. But those agreements still fall far short of meeting the need.

Around 37 percent of the population in Latin America and the Caribbean has been fully vaccinated, but access in the region has been very uneven; Cuba, Chile and Uruguay are among the most highly vaccinated countries in the world.

“We continue to urge countries with surplus doses to share these with countries in our region, where they can have life-saving impact,” said Dr. Carissa F. Etienne, director of the P.A.H.O.