FILE – In this Friday, Jan. 22, 2021, file photo, empty vials of the Pfizer-BioNTech COVID-19 vaccine are seen at a vaccination center at the University of Nevada, Las Vegas. COVID-19 vaccine makers tell Congress to expect a big jump in the delivery of doses over the coming month. The companies insisted Tuesday, Feb. 23, at a hearing that they will be able to provide enough vaccine for most Americans by summer. (AP Photo/John Locher, File)