"It's a race against the virus disappearing, and against time. At the moment, there's a 50% chance that we get no result at all", Adrian Hill, director of Oxford's Jenner Institute, said on Saturday.
According to Hill, an upcoming trial of the experimental vaccine, involving 10,000 volunteers, could return "no result" due to low transmission of COVID-19 in the British community.
Earlier, Hill’s team spoke of an 80-percent success of the vaccine, which was expected to be ready by September.
Early-stage human trials of the vaccine started on 23 April. AstraZeneca received $1.2 billion from the US government to produce 400 million doses of the vaccine. The results of the first-stage clinical trials are expected in June.
Meanwhile, pre-clinical trials of a vaccine against the coronavirus conducted by the Gamaleya Scientific Research Institute of Epidemiology and Microbiology of the Russian Health Ministry are showing good results, and human trials are expected to start by 15 June, according to Director Alexander Gintsburg.