A LEAD scientist on Oxford's coronavirus vaccine trial has said it only have a 50 per cent chance of success due to falling cases.

Project leader Professor Adrian Hill,of Oxford University’s Jenner Institute, in an interview with the Sunday Telegraph, said: "It's a race against the virus disappearing, and against time.

"We said earlier in the year that there was an 80 per cent chance of developing an effective vaccine by September.

"But at the moment, there's a 50 per cent chance that we get no result at all. We're in the bizarre position of wanting Covid to stay, at least for a little while."

Trials of the vaccine began with an initial phase of testing on 160 healthy volunteers between the ages of 18 and 55 to see if it could effectively fight off the virus.

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The study is set to progress to a second and third phase, which will involve testing up to 10,260 people and expanding the age of participants to include children and the elderly.

But if not enough people come into contact with the virus and catch it, scientists will not have enough evidence to prove it is effective and roll it out for NHS use.

Last week, the pharmaceutical company AstraZeneca announced a $1.2 billion deal with the US government to produce 400 million doses of the Oxford coronavirus vaccine.

The UK government has already agreed to pay for up to 100 million doses, adding 30 million may be ready by September if the vaccine is proved to be effective.