Covid-19 vaccine: The challenges facing the US inoculation drive

The US is the country worst hit by Covid-19 and Americans make up one in four of the world's confirmed cases. President Joe Biden is working to lower that number by ramping up the heavily delayed delivery of vaccines. He says he wants 300 million Americans vaccinated by late summer or the autumn. But it's a steep road ahead. Current vaccine shortages have been so severe that tens of thousands of appointments have been cancelled for people hoping to get their first shot.