People queue to enter an NHS Covid-19 vaccination centre in Westfield Stratford City shopping centre in east London on February 15, 2021 as Britain's largest ever vaccination programme continues. - Prime Minister Boris Johnson called Britain hitting a target of inoculating 15 million of the most vulnerable people with a first coronavirus jab "a significant milestone", as the country prepared for the next phase of its vaccination programme. (Photo by Tolga Akmen / AFP)