Immunizing children and supporting other health-related efforts—like fighting malaria, HIV, and tuberculosis—is the biggest focus of my philanthropy. I’m moved to act by the fact that roughly 5 million children under the age of 5 die every year, the vast majority of them in poor countries. Meanwhile, lifesaving tools like vaccines and medicines get developed for diseases that affect those who can pay, and not for ones that mostly affect people in poorer countries.

The U.S. government has been a crucial partner in this work. But when its aid is withdrawn—abruptly and without a plan, as has happened recently—lives are lost. I recently sent written testimony to Congress about how cuts in aid have already harmed people and will have an even worse impact in the future. And I’ve written an op-ed in the Wall Street Journal urging Congress not to make these cuts.

As a grandfather, I can’t imagine how awful it would be to lose a child, yet millions of families suffer that tragedy every year simply because of where they live. Fixing this disparity is the chief reason the Gates Foundation exists. I go to work each day thinking about how I can help close the gap.