Oxford human challenge trial to re-expose healthy volunteers to Covid

Laura Donnelly
·3 min read
volunteer is injected -  Oxford University
volunteer is injected - Oxford University

Healthy young volunteers who have previously had Covid will be deliberately exposed for a second time during “human challenge” trials.

Scientists from Oxford University are recruiting participants aged 18 to 30, to see how the immune system responds in a bid to develop better vaccines.

The research is seeking to establish what kind of immune response stops people from becoming reinfected - and future studies may examine what level of protection is given against new variants.

In the first phase of the study, up to 64 healthy participants who have previously been naturally infected with Covid will be re-exposed to the same virus, in carefully controlled conditions.

Recruitment is open to those aged between 18 and 30, who had a positive PCR test for Covid at least three months ago, and are fit and healthy.

The trial will test different doses of infections to see what levels take hold, and start replicating, without producing symptoms.

Scientists said a follow-up trial could see how the participants respond to a new variant, such as the South African type, in order to try to establish how best to protect against new threats.

Researchers said the volunteers, will be reimbursed £5,000 for their time and inconvenience in the year-long trial, which includes 17 days quarantined in a specially designed hospital suite.

Participants will be placed under close supervision, and those who develop symptoms will receive Regeneron monoclonal antibody treatment, they said.

Last week an observational study of 3,000 young people in the US, found that 10 per cent of those who had previously been infected with Covid became reinfected.

Human challenge trials are controversial, because they involve purposefully infecting a subject with a pathogen, in order to study the effects of that infection.

Doing so in controlled circumstances will allow scientists to learn more about best to boost immunity, and prevent reinfection, they said.

Helen McShane, Professor of Vaccinology at the Department of Paediatrics, University of Oxford, and Chief Investigator on the study said the findings would mean that scientists could look at “every single aspect of immunity we can possibly study” including antibodies and T cells, to establish what was needed to prevent infection, and how long it lasted.

She said: “The point of this study is to determine what kind of immune response prevents reinfection.

“It's the first time anyone with previous SARS Co-V-2 infection has been deliberately infected in this way.”

“We will be interrogating the baseline immune response in these healthy volunteers, and then looking at whether or not we can reinfect, we will be looking at the quality of that immune response, we'll look at antibodies, we'll look at T-cells, we'll look at every single aspect of immunity we can possibly study, we will look at the quantity of that immune response. And of course, critically, we will also look at durability.”

In the first phase of the trial, starting later this month, scientists will seek to establish the lowest dose of virus which is enough to take hold and start replicating in at least half of those who have previously had Covid. The second phase, in the summer, will see what happens to participants given a standard dose of virus.

Establishing the level of immune response which prevents infection could help scientists establish whether future vaccine would be effective, with fewer trials, Prof McShane suggested.

Further trials could see how participants respond to new variants, with the South African variant among those under consideration, she said.

“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,” she said.

A similar study is already ongoing, led by Imperial College London, where volunteers without a history of Covid are being infected with the virus to test vaccines and treatments.