FILE: A nurse prepares a shot as a study of a possible COVID-19 vaccine, developed by the National Institutes of Health and Moderna Inc., gets underway in Binghamton, NY, July 27, 2020. Who gets to be first in line for a COVID-19 vaccine? US health authorities hope by late next month to have some draft guidance on how to ration initial doses, but it's a vexing decision. (AP Photo/Hans Pennink)