Covid-19 ‘Challenge Trial’ Will Purposely Reinfect Adults

The new trial is focused on probing the boundaries of human immunity and the effects of the virus on the body from the moment of reinfection. Better understanding of protection from previous illness will help fast-track new treatments and vaccines, Oxford researchers say.

The first Covid-19 challenge study, led by Imperial College London infectious-disease researchers, started in March with a handful of volunteers isolated inside London’s Royal Free Hospital, part of the state-funded National Health Service. That study received a pledge of more than $45 million from the U.K. government.

Oxford’s trial is funded by the London-based Wellcome Trust, a healthcare-focused charitable foundation. As many as 64 people aged 18 to 30 years will be quarantined in staggered phases inside Oxford University Hospitals at roughly 17-day intervals, starting as soon as next month, according to

Helen McShane,

an Oxford vaccinologist who is leading the trial.

Participants must be unvaccinated and have Covid-19 antibodies from a previous infection, but be fully recovered and able to pass a rigorous health screening.

Debates about inoculating humans with live, potent viruses have gone on for centuries. In the late 1700s, British doctor Edward Jenner applied material from cowpox and smallpox lesions to children and adults and recorded the reactions. The now-famous experiments paved the way for modern vaccines.

But in the pandemic, the U.S. and other countries have steered clear of purposely infecting healthy people with the coronavirus. Critics argue the risks aren’t justified, given the broad presence of naturally circulating virus and the success of vaccines already available. What’s more, some say newer variants of the virus make the older strain used in the U.K. challenge trials less relevant. There is also a lack of proven treatments and risks from so-called “long Covid,” little-understood long-term symptoms including fatigue, memory loss and heart damage.

Challenge-trial proponents argue there is no substitute for the precision of controlled studies. They have been used for decades to study diseases including typhoid, malaria and tuberculosis and to develop vaccines. With Covid-19, Prof. McShane told journalists in a briefing last week, “We don’t know whether someone has not been infected because they haven’t been exposed or [because] they have protective immunity.” Controlling exposure will help with those questions, she said.

The first phase of the Oxford-led trials will test virus dosages required for reinfection, administered through the nose. Phase two will chart immune response, including protection via prior infection. No vaccines will be used in either phase.

Volunteers will be tracked for a year. They will be paid around £5,000, equivalent to $6,917, for their time in quarantine and for follow-ups, Prof. McShane said. Oxford’s partners include U.K.-based drug-testing company hVIVO Services Ltd., which has experience in challenge trials and is also involved in the Imperial College study.

Write to Jenny Strasburg at [email protected]