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Challenge Trial Testing Covid-19 Reinfection

SARS-Cov-2 virus

Scanning electron microscope image of SARS-Cov-2 virus, in orange, emerging from cells (NIAID, Flickr)

19 Apr. 2021. A clinical trial is underway testing immune responses from new Covid-19 infections in volunteers previously infected with the virus. The human challenge trial is conducted by University of Oxford in the U.K., funded by the Wellcome Trust, a medical research foundation in London.

A team led by Helen McShane, a vaccinology professor at Oxford, aims to learn more about the body’s immune response to the SARS-CoV-2 virus when infected for a second time. The researchers are particularly interested in the nature of that immune response, whether by antibodies, T-cells, or a combination. A challenge trial with human volunteers, say the researchers, is the most direct and efficient way to discover this immune response. As reported in Science & Enterprise in October 2020, Imperial College London and the company hVIVO began a challenge trial to test then-experimental Covid-19 vaccines.

The new study is enrolling 64 healthy individuals, age 18 to 30, who were previously infected with the SARS-CoV-2 virus. Participants will receive carefully metered doses of the original SARS-CoV-2 strain, while quarantined in a clinic and watched by researchers for 17 days. During this time, participants will be monitored for changes in their condition, including MRI heart scans and CT lung scans, then tracked with eight medical checkups in the next 12 months. Any new infections will be treated with the Regeneron antibody cocktail.

The study team is looking first in a subset of the sample for the minimum viral quantity that enables the virus to replicate in previously infected people, but cause few if any symptoms. Once that minimal viral level is established, the full group will be injected with the virus to determine immune responses.

Measure immune response over time

“In phase two, we will explore two different things,” says McShane in a university statement. “First, we will define very carefully the baseline immune response in the volunteers, before we infect them. We will then infect them with the dose of virus chosen from the first study and measure how much virus we can detect after infection. We will then be able to understand what kind of immune responses protect against re-infection. Second, we will measure the immune response at several time points after infection so we can understand what immune response is generated by the virus.”

“When we re-infect these participants, we will know exactly how their immune system has reacted to the first Covid infection,” adds McShane, “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.”

Shobana Balasingam, a vaccines advisor at Wellcome Trust notes, “This study has the potential to transform our understanding by providing high-quality data on how our immune system responds to a second infection with this virus. ‘The findings could have important implications for how we handle Covid-19 in the future, and inform not just vaccine development but also research into the range of effective treatments that are also urgently needed.”

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