ALISTAIR SMOUT A 90-year-old grandmother became the world's first person to receive a fully-tested COVID-19 shot on Tuesday, as Britain began mass-vaccinating its people in a global drive that poses one of the biggest logistical challenges in peacetime history. Health workers started inoculating the most vulnerable with the vaccine developed by Pfizer and BioNTech, with the country a test case for the world as it contends with distributing a compound that must be stored at -70C (-94F). Margaret Keenan, who turns 91 in a week, was the first to receive the shot, at a hospital in Coventry, central England. "It's…