Another proposal, put forward in a letter backed by the Center for Strategic and International Studies (CSIS), calls for the United States to donate 10 percent of its excess doses over the summer, moving to 50 percent by the end of the year, and argues that Biden should deliver a speech this spring to make the case to the American people... The United States will probably have “at least 300 million excess doses or more” by the end of July, the Duke paper’s authors estimate, even as vaccination programs are extended to the vast majority of U.S. children. The estimate is based on the assumption that the vaccine developed by AstraZeneca receives emergency-use authorization and the Johnson & Johnson vaccine is used widely, despite rare side effects.