The U.K. launched its largest-ever immunization program Tuesday. Health officials began dispensing doses of the Pfizer and BioNTech coronavirus vaccine, first vaccinating healthcare workers and residents over the age of 80.

LONDON, ENGLAND – DECEMBER 08: A nurse administers the Pfizer-BioNTech COVID-19 vaccine at Guy’s Hospital at the start of the largest ever immunisation programme in the UK’s history on December 8, 2020 in London, 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 Frank Augstein – Pool / Getty Images)