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Oxford researchers are seeking participants for a trial to discover what happens when people who have either already had Covid-19 or who have been vaccinated are exposed to the original strain of virus.

Researchers at the University of Oxford are looking for volunteers to take part in a human challenge trial to look at what kind of immune response can stop people from becoming infected with the original strain of the virus. The trial began in in April 2021 and the researchers are working with healthy young participants to study how the immune system responds to the virus.

A human challenge trial in medical research is a carefully controlled study that involves purposefully infecting a subject with a pathogen or bug, in order to study the effects of that infection.

Helen McShane, Professor of Vaccinology at the Department of Paediatrics, University of Oxford and Chief Investigator on the study said: 'A human challenge model is where, under a very carefully controlled conditions we deliberately expose healthy volunteers to a bug or pathogen.

'The aim of this trial is to find out what level of immune response - antibodies and T cells - we need in our bodies to prevent infection when healthy people are exposed to the virus. This is the immune response we then need to induce with a new vaccine.

'We have learned a lot about Covid over the past two years, but the emergence of new variants means that we will probably have to keep refining the vaccines. If we know what level of immune response we need the vaccine to induce it will make future vaccine development much quicker and much more efficient.'

The first phase of the study began in April 2021, and is currently establishing the lowest dose of virus which, in approximately 50% of people who have previously been naturally infected or vaccinated, can take hold and start replicating but produce little or no symptoms. In the second phase of the study, all participants will be infected with the standardised dose of virus which was established in phase one.

The virus used in the study will be the original strain from Wuhan, China. The participants will be quarantined in a specially designed hospital suite for a minimum of 17 days under the care of the research team. They will undergo numerous medical tests including CT scans of the lungs and MRI scans of the heart. The risks to participants will minimised by making sure that those who take part are completely fit and well and, if applicable, have completely recovered from their first infection with Covid.

Any participants who develop any symptoms will be given medical treatment with the Regeneron monoclonal antibody treatment (known as Ronapreve). They will only be discharged from the quarantine unit when they are no longer infected and not at risk of infecting others. The full length of the study will be 12 months, including a minimum of five follow-up appointments after discharge. Participation in the study is completely voluntary.

Participants should be between 18-30 years old in excellent health who either 1) have already had Covid-19 and are either vaccinated or unvaccinated against Covid, or 2) no previous history of Covid-19 infection but have received a vaccine against Covid.

For more information on the trial and for an insight into what participants can expect, please watch our video, which includes interviews with current participants.

The study is funded by the Wellcome Trust.