Screengrab taken from undated video issued by Johnson and Johnson showing vials of the Janssen COVID-19 vaccine. The single-shot vaccine, which has been developed by Johnson and Johnson’s pharmaceutical arm Janssen, is 66 percent effective at preventing moderate to severe Covid-19 but offers high protection against people needing to go to hospital, trial results show. The UK has ordered 30 million doses of the vaccine, with the option of 22 million more.