Volunteers will be reinfected for trial

‘‘When we reinfect 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

University of Oxford

Scientists will attempt to reinfect healthy volunteers who have recovered from Covid-19 infection in a new trial by the University of Oxford.

They are starting the first human challenge trial of its kind today to look at what kind of immune response could stop people becoming reinfected and how the immune system reacts the second time round.

Participants will be reimbursed £5000 (NZ$9700) for the inconvenience of participating in the trial, which requires a 17-day hospital stay and regular follow-up for 12 months.

A number of observational studies have shown extremely low rates of reinfection among people who have previously tested positive for Covid-19 but in those trials it was not possible to be certain whether those people have had another brush with the virus and fought it off or simply not encountered it a second time.

Helen McShane, professor of vaccinology at the University of Oxford and the study’s chief investigator, said: ‘‘When we reinfect 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. As well as enhancing our basic understanding this may help us to design tests that can accurately predict whether people are protected.’’

By establishing what level of antibodies are needed to fight off the virus, the trial could also pave the way for faster vaccine approval. Should a vaccine be shown to prompt an antibody response of that level, regulators might approve it on that basis, as they do for other diseases, rather than waiting for the results of phase three trials comparing vaccinated and unvaccinated patients.

The trial will have two phases. The first, involving 24 people and starting this month, will set out to establish the lowest dose of virus that can take hold in approximately 50 per cent of people who have previously been naturally infected, with little or no symptoms. The second, expected to start in the summer and with about 40 participants, will infect them with that dose and observe their immune response.