The COVID-19 Uninsured Program, administered by the Health Resources and Services Administration (HRSA), reimbursed providers for administering COVID-19 vaccines to uninsured US adults from December 11, 2020, through April 5, 2022. Using HRSA claims data covering forty-two states, we estimated that the program funded about 38.9 million COVID-19 vaccine doses, accounting for 5.7 percent of total doses distributed and 10.9 percent of doses administered to adults ages 19-64.