The immune response needed to protect people against reinfection with the coronavirus will be explored in a new human challenge trial, researchers have revealed.

Human challenge trials involve deliberately exposing healthy people to a disease-causing organism in a carefully controlled manner, and have proved valuable in understanding and tackling myriad conditions from malaria to tuberculosis and gonorrhoea.

The first human challenge trials for Covid began this year, with the study – a partnership led by researchers at Imperial College London among others – initially looking at the smallest amount of virus needed to cause infection among people who have not had Covid before.

“The point of this study is to determine what kind of immune response prevents reinfection,” said Helen McShane, a professor of vaccinology at the University of Oxford, and chief investigator on the study.

McShane said the team would measure the levels of various components of participants’ immune response – including T-cells and antibodies – and then track whether participants became reinfected when exposed to the virus.

Participants must be healthy, at low risk from Covid, aged between 18 and 30, and must have been infected with the coronavirus at least three months before joining the trial. As well as having previously had a positive Covid PCR test, they must also have antibodies to Covid. Given the timing criteria, McShane said it was likely most participants would have previously been infected with the original strain of the virus.

The first phase of the trial will initially involve 24 participants split into dose groups of three to eight people who will receive, via the nose, the original strain of coronavirus. The idea is to start with a very low dose and, if necessary, increase the dose – up to a point – between groups.

“Our target is to have 50% of our subjects infected but with no, or only very mild, disease,” said McShane, adding that once the dose required to achieve this is determined it will be administered to 10-40 other participants to confirm the dose.

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Thanks to Heinz V. Hoenen.  Follow him on twitter: @HeinzVHoenen