RFK Jr. announced a halt to all U.S. funding for the global Gavi vaccine alliance. One expert calls it a "travesty and a nightmare."

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.

Global vaccine group Gavi has more than $9 billion for its work over the next five years helping to immunize the world's poorest children, including money raised at a Brussels fundraising summit, it said on Wednesday.