The tests get underway today.
Healthy adults aged between 18 and 55 will be among the first to try out a new potential coronavirus vaccine.
They'll be monitored to see whether the jab is safe, before it's then tested on the elderly.
The tests are being carried out by Scientists at the University of Oxford, in the UK.
The lead researcher at the University previously said it has an 80 per cent chance of working.
However, Professor Adam Finn from Bristol University, who is helping with trials, isn't as confident.
''Most vaccines don't work, and only a minority come through and are successful in the end'', he said.
''I think this vaccine has a good chance of success, but I think we need lots of horses in the race to be sure that at least a few reach the finishing line''.
Sky News reports The Oxford vaccine, called ChAdOx1 nCoV-19, is made from a harmless chimpanzee virus that has been genetically engineered to carry part of the coronavirus.
The technique has already been shown to generate strong immune responses in other diseases.
