Two volunteers were injected, the first of more than 800 people recruited for the study.
Half will receive the Covid-19 vaccine, and half a control vaccine which protects against meningitis but not coronavirus.
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.
“Of course, we have to test it and get data from humans. We have to demonstrate it actually works and stops people getting infected with coronavirus before using the vaccine in the wider population.”
Prof Gilbert previously said she was “80% confident” the vaccine would work, but now prefers not to put a figure on it, saying simply she is “very optimistic” about its chances.
So how does the vaccine work?
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.
How will they know if it works?*
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.
