The University of Oxford said Monday it has launched a trial in which people who have already had COVID-19 are deliberately reinfected.
The carefully controlled study will look at the kind of immune response mounted by the volunteers.
The scientists will know "exactly when the second infection occurs, and exactly how much virus they got," Helen McShane, a professor of vaccinology, said in a statement.
She said the trial "may help us to design tests that can accurately predict whether people are protected" after a prior infection.
Anyone who suffers symptoms will receive the Regeneron antibody treatment used to treat Covid-19 patients.
The University of Oxford's "first-of-a-kind" tests are funded by the Wellcome Trust.
At the start of the trial, up to 64 fit and healthy volunteers aged 18 to 30 will be deliberately reinfected with the original Wuhan strain.
They will be quarantined for at least 17 days in a special hospital suite, having lung and heart scans. They will then have follow-up appointments and be monitored for a year.
"This study has the potential to transform our understanding by providing high-quality data," said Shobana Balasingam, vaccines senior research advisor at Wellcome.
The trial's initial phase will look at the minimum dose that allows the virus to start replicating without symptoms in some 50 percent of volunteers.
Then in the second phase, another group of volunteers will all receive this established minimum dose.
The trial comes as a London hospital has isolated a group of healthy volunteers while exposing them to the virus, in a world first.
That began in March and is being carried out in collaboration between Imperial College London and the company hVIVO at the Royal London Hospital.
Those who have been infected in a controlled way are monitored to see how their illness progresses and how drugs and vaccines could work against it.
