The vaccine, RotaTeq, protects against a deadly form of diarrhea called rotavirus, which kills 215,000 children under the age of five each year, according to World Health Organization estimates.

Merck agreed to sell the RotaTeq vaccine to Gavi, the Vaccine Alliance at a discounted price in 2011. Through Gavi, over the past six years Merck has delivered 30 million doses of the vaccine to four African countries—Burkina Faso, Ivory Coast, Mali, and São Tomé and Príncipe—at about $3.50 per dose, NPR reports.

Now, however, Merck has told Gavi that it will not deliver a third of the doses needed for 2018 and 2019, and it will cease all deliveries to these countries in 2020. This will leave more than 2.5 million children vulnerable just within these three years, Gavi told NPR.

Merck told NPR the decision to end these deliveries was due to supply shortages related to “country-specific requirements, unanticipated manufacturing issues and packaging challenges that put greater stress on our already strained packaging capacity.”

“This was difficult decision for us, which did not come lightly,” Merck told NPR via email. “We would like to express our deepest regret to all of the parties involved and have offered to assist and work with UNICEF, Gavi and affected countries through the transition to alternative images [versions] of rotavirus vaccines.”

While Merck steps out of the African market, it’s also begun selling RotaTeq to China, where NPR reports each dose could go for upwards of $40—a much larger profit margin than in Africa. Merck told NPR the decision to sell RotaTeq in China is per “a binding agreement we signed with a local vaccine company in 2012.”