Healthy adults aged between 18 and 55 will be among the first to try out a new potential COVID-19 vaccine.
They'll be monitored to see whether the jab is safe, before it's then tested on the elderly.
The lead researcher at Oxford University previously said it has an 80% chance of working.
Professor Adam Finn from Bristol University, who is helping with trials, isn't as confident:
"Most vaccines don't work - the ones that we try out. Only a minority that come through are successful in the end, I think this vaccine has a good chance of success, but I think we need a lot of horses in the race to be sure of a few reaching the finish line."