Healthcare personnel perform CPR on a patient inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center as the United States nears 300,000 COVID-19 deaths, in Houston, Texas, U.S., December 12, 2020. Picture taken December 12, 2020. REUTERS/Callaghan O'Hare

Healthcare personnel check to see if a patient still has a pulse inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center as the United States nears 300,000 COVID-19 deaths, in Houston, Texas, U.S., December 12, 2020. Picture taken December 12, 2020. REUTERS/Callaghan O'Hare

Gabriel Cervera watches a patient's heart rate drop while working inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center as the United States nears 300,000 COVID-19 deaths, in Houston, Texas, U.S., December 12, 2020. Picture taken December 12, 2020. REUTERS/Callaghan O'Hare

Healthcare personnel attend to a patient in cardiac arrest inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center as the United States nears 300,000 COVID-19 deaths, in Houston, Texas, U.S., December 12, 2020. REUTERS/Callaghan O'Hare

A patient who died lays in a body bag inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center as the United States nears 300,000 COVID-19 deaths, in Houston, Texas, U.S., December 12, 2020. Picture taken December 12, 2020. REUTERS/Callaghan O'Hare

Gabriel Cervera calls the family of a patient who died, as healthcare personnel work inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center in Houston, Texas, U.S., December 12, 2020. Picture taken December 12, 2020. REUTERS/Callaghan O'Hare TPX IMAGES OF THE DAY

Sandra Lindsay, a nurse at Long Island Jewish Medical Center, is inoculated with the coronavirus disease (COVID-19) vaccine by Dr. Michelle Chester from Northwell Health at Long Island Jewish Medical Center in New Hyde Park, New York, U.S., December 14, 2020. Mark Lennihan/Pool via REUTERS TPX IMAGES OF THE DAY

Members of the media are seen as Dr Yves Duroseau from Lennox Hill Hospital is inoculated with the Pfizer coronavirus disease (COVID-19) vaccine by Dr Michelle Chester from Northwell Health at Long Island Jewish Medical Center, in New Hyde Park, New York, U.S., December 14, 2020. REUTERS/Brendan Mcdermid

Boxes containing the Pfizer-BioNTech COVID-19 vaccine are prepared to be shipped at the Pfizer Global Supply Kalamazoo manufacturing plant in Portage, Michigan, U.S., December 13, 2020. Morry Gash/Pool via REUTERS TPX IMAGES OF THE DAY

Boxes containing Pfizer's COVID-19 vaccine are unloaded from air shipping containers and scanned at UPS Worldport, in Louisville, Kentucky, December 13, 2020. Michael Clevenger/Pool via REUTERS

Boxes containing Pfizer's COVID-19 vaccine are unloaded from air shipping containers at UPS Worldport, in Louisville, Kentucky, December 13, 2020. Michael Clevenger/Pool via REUTERS

UPS employees move one of two shipping containers of the Pfizer COVID-19 vaccine on ramp at Louisville Muhammad Ali International Airport in Louisville, Kentucky, December 13, 2020. Michael Clevenger/Pool via REUTERS

Boxes containing the Pfizer-BioNTech COVID-19 vaccine are prepared to be shipped at the Pfizer Global Supply Kalamazoo manufacturing plant in Portage, Michigan, U.S., December 13, 2020. Morry Gash/Pool via REUTERS

Vaccination record cards are prepared for distribution as healthcare workers take part in a rehearsal for the administration of the Pfizer coronavirus disease (COVID-19) vaccine at Indiana University Health in Indianapolis, Indiana, U.S., December 11, 2020. REUTERS/Bryan Woolston

Alan Murcia comforts his wife, Corina Murcia, inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center in Houston, Texas, U.S., December 12, 2020. REUTERS/Callaghan O'Hare TPX IMAGES OF THE DAY

Theresa Ogunjimi, a registered nurse, rests for a moment inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center, as the United States nears 300,000 COVID-19 deaths, in Houston, Texas, U.S., December 12, 2020. Picture taken December 12, 2020. REUTERS/Callaghan O'Hare

Healthcare personnel work inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center as the United States nears 300,000 COVID-19 deaths, in Houston, Texas, U.S., December 12, 2020. Picture taken December 12, 2020. REUTERS/Callaghan O'Hare

Healthcare personnel work inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center, as the United States nears 300,000 COVID-19 deaths, in Houston, Texas, U.S., December 12, 2020. REUTERS/Callaghan O'Hare

Alvino Flores watches television inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center in Houston, Texas, U.S., December 12, 2020. REUTERS/Callaghan O'Hare

Healthcare personnel work inside a coronavirus disease (COVID-19) unit at United Memorial Medical Center as the United States nears 300,000 COVID-19 deaths, in Houston, Texas, U.S., December 12, 2020. REUTERS/Callaghan O'Hare

People wait in line at the St. Clements Food Pantry for food during the coronavirus disease (COVID-19) pandemic in the Manhattan borough of New York City, New York, U.S., December 11, 2020. REUTERS/Carlo Allegri

People wait in line at the St. Clements Food Pantry for food during the coronavirus disease (COVID-19) pandemic in the Manhattan borough of New York City, New York, U.S., December 11, 2020. REUTERS/Carlo Allegri

Healthcare workers take part in a rehearsal for the administration of the Pfizer coronavirus disease (COVID-19) vaccine at Indiana University Health in Indianapolis, Indiana, U.S., December 11, 2020. REUTERS/Bryan Woolston TPX IMAGES OF THE DAY

Evelia De La Cruz, a hospital housekeeper at Roseland Community Hospital, disinfects the room where a coronavirus disease (COVID-19) positive patient died in the intensive care unit on the South Side of Chicago, Illinois, U.S. December 1, 2020. Picture taken December 1, 2020. REUTERS/Shannon Stapleton TPX IMAGES OF THE DAY

Evelia De La Cruz, a hospital housekeeper at Roseland Community Hospital, stands while wearing a face mask to protect against the coronavirus disease (COVID-19) before cleaning on the South Side of Chicago, Illinois, U.S., December 4, 2020. Picture taken December 4, 2020. REUTERS/Shannon Stapleton TPX IMAGES OF THE DAY

Evelia De La Cruz, a hospital housekeeper at Roseland Community Hospital, cleans for coronavirus disease (COVID-19) positive patient Bruce Shackleford in his isolation room on the South Side of Chicago, Illinois, U.S., December 8, 2020. Picture taken December 8, 2020. REUTERS/Shannon Stapleton

Pharmacy supervisor Kevin Weissman opens the door of a special freezer that will hold the Pfizer vaccine at LAC USC Medical Center during the outbreak of the coronavirus disease (COVID-19) in Los Angeles, California, U.S., December 10, 2020. REUTERS/Mike Blake

Pharmacy supervisor Kevin Weissman displays a special glove that is needed to handle the Pfizer vaccine when removed from a freezer unit at LAC USC Medical Center during the outbreak of the coronavirus disease (COVID-19) in Los Angeles, California, U.S., December 10, 2020. REUTERS/Mike Blake

Bruce Shackleford, a coronavirus disease (COVID-19) positive patient, sits in his isolation room at Roseland Community Hospital on the South Side of Chicago, Illinois, U.S., December 8, 2020. REUTERS/Shannon Stapleton TPX IMAGES OF THE DAY

Registered nurse Trina Owens tends to Andre Johnson, a coronavirus disease (COVID-19) positive patient, in his isolation room on the acute care unit at Roseland Community Hospital on the South Side of Chicago, Illinois, U.S., December 8, 2020. REUTERS/Shannon Stapleton

A Christmas tree dressed as a nurse, as the global outbreak of the coronavirus disease (COVID-19) continues, stands at the entrance to the intensive care unit at Roseland Community Hospital on the South Side of Chicago, Illinois, U.S., December 8, 2020. REUTERS/Shannon Stapleton

St Mary Medical Center staff work inside a triage tent to handle the overflow at its 200 bed hospital during the outbreak of the coronavirus disease (COVID-19) in Apple Valley, California, U.S., December 8, 2020. REUTERS/Mike Blake TPX IMAGES OF THE DAY

Patient Amy Garcia is help into the emergency room by anaesthesia assistant Ryan Preston as St Mary Medical Center resorts to using triage tents outside to handle the overflow at its 200 bed hospital during the outbreak of the coronavirus disease (COVID-19) in Apple Valley, California, U.S., December 8, 2020. REUTERS/Mike Blake

Emergency department team leader Jahmaal Willis sits next to a walled off area separating the emergency room at St Mary Medical Center during the outbreak of the coronavirus disease (COVID-19) in Apple Valley, California, U.S., December 8, 2020. REUTERS/Mike Blake