The global death toll from COVID-19 topped 5 million on Monday, less than two years into a crisis that has not only devastated poor countries but also humbled wealthy ones with first-rate health care systems. Together, the US, the European Union, Britain and Brazil — all upper-middle- or high-income countries — account for one-eighth of the world’s population but nearly half of all reported deaths. The U.S. alone has recorded over 740,000 lives lost, more than any other nation.