Healthy, young volunteers who have previously had Covid-19 will be deliberately exposed to the virus for a second time to see how the immune system reacts.

Oxford University researchers have launched a "human challenge" trial to look at what happens when someone who has recovered from coronavirus is re-exposed to the virus.

They will aim to determine what dose of virus is needed to re-infect after natural infection, how the immune system responds, and what this may mean for developing protective immunity against the disease.

The Wellcome Trust study is expected to start this month after receiving ethics approval and will recruit people aged 18 to 30 who have previously been naturally infected with the disease.

They will be re-exposed to the virus in a safe and controlled environment while a team of researchers monitor their health.

Human challenge studies have played a key role in furthering the development of treatments for diseases such as malaria, TB, typhoid, cholera and flu.

The study's chief investigator Helen McShane, professor of vaccinology at Oxford's department of paediatrics, said: "Challenge studies tell us things that other studies cannot because, unlike natural infection, they are tightly controlled.

“When we re-infect these participants, we will know exactly how their immune system has reacted to the first Covid infection, exactly when the second infection occurs, and exactly how much virus they got.”

While Covid-19 infections have been rare, recent research suggests prior infection may not fully protect young people against reinfection.

The observational study, published in the Lancet involving US Marine Corps members mostly aged 18 to 20, showed that between May and November last year, around 10% of participants who had previously caught coronavirus became reinfected.

The Oxford study will take phase in two phases.

The first phase, involving 64 volunteers, aims to establish the lowest dose of virus which can take hold and start replicating.

Once the dosing amount is established, it will be used to infect participants in the second phase of the study, which is expected to start in the summer.

Prof McShane said: "We will measure the immune response at several time points after infection so we can understand what immune response is generated by the virus.

"A challenge study allows us to make these measurements very precisely because we know exactly when someone is infected.

"The information from this work will allow us to design better vaccines and treatments, and also to understand if people are protected after having Covid, and for how long."