A nurse in the U.K. prepares to administer Covid-19 vaccinations earlier this month. Canadian health officials on Wednesday authorized the use of the Pfizer-BioNTech vaccine.

TRURO, ENGLAND – DECEMBER 09: A staff nurse at the Royal Cornwall Hospital prepares to administer Covid-19 vaccinations as the hospital began their vaccination programme on December 9, 2020 in Truro, United Kingdom. More than 50 hospitals across England were designated as covid-19 vaccine hubs, the first stage of what will be a lengthy vaccination campaign. NHS staff, over-80s, and care home residents will be among the first to receive the Pfizer/BioNTech vaccine, which recently received emergency approval from the country’s health authorities. (Photo by Hugh Hastings/Getty Images)