TORONTO -- A new study at the University of Oxford will see patients who have already had COVID-19 re-exposed to the virus that causes it, in order to gauge their immune response and determine how to best protect against reinfection.

The “human challenge trial”, which launches this month, will take place in two phases with different participants in each phase. The first will establish the lowest dose of virus which can infect a person and start replicating, but produce little or no symptoms. In the second part, likely to start this summer, participants will be infected with the dose of virus as established in the first phase.

A human challenge trial is a pharmaceutical study in which a human subject is intentionally exposed to a disease or virus, as opposed to merely testing for a side effect of the treatment being studied.

“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,” Helen McShane, professor of vaccinology at Oxford, said in a statement. “As well as enhancing our basic understanding, this may help us to design tests that can accurately predict whether people are protected.”

The study will involve healthy participants aged 18-30 who have previously been naturally infected with COVID-19 and have completely recovered. The virus used in the study will be the original strain that emerged from Wuhan, China, and participants will be quarantined in a specially designed hospital suite for a minimum of 17 days following infection, the statement said.

Participation is voluntary and any subjects who develop COVID-19 symptoms will be treated with the Regeneron monoclonal antibody treatment, and discharged from quarantine when they are no longer infected. The study is expected to last 12 months in total.

“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 McShane.