An Oxford University vaccine for Covid-19 has only a 50 per cent chance of success because there are so few cases.
Adrian Hill, who is co-leader of the project, said that a trial involving 10,000 people could return no result because the virus was not prevalent enough for volunteers to catch. Last month the university said that there was an 80 per cent chance of success.
Professor Hill said that out of the 10,000 he expected fewer than 50 to catch the virus. If fewer than 20 test positive, the result may be useless.
Ministers have said that 30 million doses of a successful vaccine could be ready by September but Professor Hill, director of the university’s Jenner Institute, told The Sunday Telegraph: “It