Gavi is a public-private partnership including WHO, UNICEF, the Gates Foundation and the World Bank, and it is estimated that the vaccination programs have saved 18 million lives. The United States has long been one of its biggest supporters; before President Donald Trump’s re-election, the country had pledged $1 billion through 2030.

U.S. Health Secretary Robert F. Kennedy Jr. said the organization has “ignored the science" and “lost the public trust.”

Gavi works to expand access to vaccines for children in some of the world’s poorest countries. Health experts say the move could have deadly consequences.