Thanks to Gavi, the Vaccine Alliance, more than 1 billion children have been immunized against the world’s deadliest diseases, like tuberculosis and malaria. Now the U.S. government is reportedly planning to end its support for Gavi—support that’s been critical to this progress for nearly 25 years. It breaks my heart to think that more than a million children in low-income countries could die over the next five years because of this decision. It’s no exaggeration to say that the world’s success in immunizing children is one of the greatest achievements in history. It’s also one of the hardest-won. Mothers around the world line up for hours in the heat to get vaccines for their children, women travel through mountains on foot to administer them, and thousands of scientists dedicate their lives to developing them—all because there’s nothing more important than saving the life of a child. Leaders must reconsider the plan to end support for Gavi. Unraveling one of the most effective systems in global health would be an absolutely devastating choice.