According to the British Broadcasting Corporation (BBC), the design of the trial means volunteers will not know which vaccine they are getting, though doctors will.

Elisa Granato, one of the two who received the jab, told the BBC: “I’m a scientist, so I wanted to try to support the scientific process wherever I can.”

The vaccine was developed in under three months by a team at Oxford University. Sarah Gilbert, professor of vaccinology at the Jenner Institute, led the pre-clinical research.

“Personally I have a high degree of confidence in this vaccine,” she said.

Professor Gilbert previously said she was “80 per cent confident” the vaccine would work, but now prefers not to put a figure on it, saying simply she is “very optimistic” about its chances.

The vaccine is made from a weakened version of a common cold virus (known as an adenovirus) from chimpanzees that has been modified so it cannot grow in humans.

The Oxford team has already developed a vaccine against Mers, another type of coronavirus, using the same approach and that had promising results in clinical trials.

Notably, the only way the team will know if the COVID-19 vaccine works is by comparing the number of people who get infected with coronavirus in the months ahead from the two arms of the trial.

Professor Andrew Pollard, director of the Oxford Vaccine Group, who is leading the trial, said: “We’re chasing the end of this current epidemic wave. If we don’t catch that, we won’t be able to tell whether the vaccine works in the next few months. But we do expect that there will be more cases in the future because this virus hasn’t gone away.”