UK trials set to re-expose people to virus

Move to better understand immune system reaction, help design vaccines

People who have recovered from COVID-19 disease will be deliberately re-exposed to the novel coronavirus that causes it in medical trials that start this week in the United Kingdom.

The so-called challenge trials, which are being led by the University of Oxford, will look at how much protection people have against reinfection, and against developing the disease for a second time.

The Reuters news agency said the study, which started on Monday, differs from challenge trials approved in February by medical regulator, which are being conducted by Imperial College London because they involve people who have not previously been infected with the virus.

Reuters quoted Helen McShane, a University of Oxford vaccinologist and chief investigator on the latest study, as saying: "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 scientists also hope to understand which immune responses protect against reinfection.

Researchers will start by seeking the lowest dose of novel coronavirus needed to cause an infection in someone who has previously been infected.

They hope that, by establishing the level of antibodies needed to fight off reinfection, they will open the door to faster vaccine approval, because vaccines that trigger an immune response at the identified level will be known to be adequate.

The first phase of the Oxford trials will involve up to 64 healthy participants aged between 18 and 30 who had COVID-19 at least three months before they will be given low doses of the virus. The second phase, which will be held during the summer, will involve people being given larger doses.

The Times newspaper noted that participants will each earn 5,000 pounds ($6,900) for taking part. They will have to spend 17 days in hospital and undergo regular follow-up appointments for 12 months.

Previous observational studies have suggested that very few people who have been previously infected with the novel coronavirus subsequently test positive for COVID-19 disease.

McShane said on Radio 4's Today program she is confident those taking part will not be in serious danger, and will not run the risk of developing long COVID.

"To the best of our knowledge, we think the risk of that is extremely unlikely," she said. "And the reason for that is these people have already had one infection with COVID, where they fully recovered from it."

The Times newspaper quoted Chris Chiu, the professor who is leading the Imperial College London challenge trials, as saying the two pieces of research should combine to show "how reinfection differs from a first infection with this virus, which may have important implications for how the pandemic is managed going forward".

The BBC said participants in the Oxford trials, which are being funded by the Wellcome Trust, will be exposed to a laboratory-grown virus that is the same at the original strain of novel coronavirus.

Challenge trials have previously been used to increase scientists' understanding of other diseases; including cholera, influenza, malaria, and typhoid.