Healthy, young volunteers will be infected with coronavirus to test vaccines and treatments in the world's first Covid-19 "human challenge" study, which will take place in the UK.
The study, which has received ethics approval, will start in the next few weeks and recruit 90 people aged 18-30.They will be exposed to the virus in a safe and controlled environment while medics monitor their health.
The UK has given doses of a Covid vaccine to more than 15 million people.
Human challenge studies have played a vital role in pushing the development of treatments for a number of diseases, including malaria, typhoid, cholera and flu.
The trials will help scientists work out the smallest amount of coronavirus needed to cause infection, and how the body's immune system reacts to it.