British scientists have launched a trial which will deliberately expose participants who have already had COVID-19 to the virus again to examine immune responses.
Britain became the first country in the world to give the go-ahead for so-called "challenge trials" in humans, in which volunteers are deliberately exposed to COVID-19 to advance research into the disease, in February.
However the study launched on Monday differs from that idea as it seeks to reinfect people who have already had COVID-19 in a bid to deepen understanding about immunity, rather than infecting candidates for a first time.
"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," said Oxford University vaccinologist Helen McShane.
She added that the work would help understanding of what immune responses protect against reinfection.
Scientists have used human challenge trials for decades to learn more about diseases such as malaria, flu, typhoid and cholera, and to develop treatments and vaccines.
The first stage of the trial will seek to establish the lowest dose of the coronavirus needed in order for it to start replicating in about 50 per cent of participants, while producing few to no symptoms.
A second phase, starting in the northern summer, will infect different volunteers with that standard dose.
In phase one, up to 64 healthy participants, aged 18-30, who were infected with coronavirus at least three months ago will be reinfected with the original strain of SARS-CoV-2.
They will then quarantine for at least 17 days and be monitored. Anyone who develops symptoms will be given antibody treatment.