People wait in line for the opening of a 24-hour, walk-up COVID-19 vaccination clinic hosted by the Black Doctors COVID-19 Consortium at Temple University's Liacouras Center in Philadelphia, Friday, Feb. 19, 2021. Efforts to vaccinate Americans against COVID-19 have been stymied by a series of winter storms and outages in parts of the country not used to extreme cold weather, and hobbled transportation hubs and highways. (AP Photo/Matt Rourke, File)

People stand near freezers used to store Pfizer-BioNtech's COVID-19 vaccine at a Pfizer manufacturing site, Friday, Feb. 19, 2021, in Portage, Mich. Efforts to vaccinate Americans against COVID-19 have been stymied by a series of winter storms and outages in parts of the country not used to extreme cold weather, and hobbled transportation hubs and highways. (AP Photo/Evan Vucci)

FILE - In this Dec. 20, 2020, file photo, boxes containing the Moderna COVID-19 vaccine are prepared to be shipped at the McKesson distribution center in Olive Branch, Miss. Efforts to vaccinate Americans against COVID-19 have been stymied by a series of winter storms and outages in parts of the country not used to extreme cold weather, and hobbled transportation hubs and highways. (AP Photo/Paul Sancya, Pool, File)

FILE - In this Feb. 15, 2021, file photo, an electronic message board advises drivers of potential congestion as they drive over snow on Interstate 55 in north Jackson, Miss. Efforts to vaccinate Americans against COVID-19 have been stymied by a series of winter storms and outages in parts of the country not used to extreme cold weather, and hobbled transportation hubs and highways. (AP Photo/Rogelio V. Solis, File)

FILE - In this Dec. 20, 2020, file photo, boxes containing the Moderna COVID-19 vaccine are prepared to be shipped at the McKesson distribution center in Olive Branch, Miss. Efforts to vaccinate Americans against COVID-19 have been stymied by a series of winter storms and outages in parts of the country not used to extreme cold weather, and hobbled transportation hubs and highways. (AP Photo/Paul Sancya, Pool, File)

FILE - In this Dec. 20, 2020, file photo, FedEx trucks are parked at the loading dock outside the McKesson distribution center in Olive Branch, Miss. Efforts to vaccinate Americans against COVID-19 have been stymied by a series of winter storms and outages in parts of the country not used to extreme cold weather, and hobbled transportation hubs and highways. (AP Photo/Paul Sancya, Pool, File)

FILE - In this Dec. 20, 2020, file photo, boxes containing the Moderna COVID-19 vaccine are prepared to be shipped at the McKesson distribution center in Olive Branch, Miss. Efforts to vaccinate Americans against COVID-19 have been stymied by a series of winter storms and outages in parts of the country not used to extreme cold weather, and hobbled transportation hubs and highways. (AP Photo/Paul Sancya, Pool)