UK COVID-19 human challenge trials need participants. International volunteers are ready to heed the call

By Zacharia Kafuko.

Last month, the UK government approved a bold innovation that will take us closer to finally ending the COVID-19 pandemic: human challenge trials, which involve deliberately exposing volunteers to the coronavirus to help researchers study the disease. The first trial began in London in early March, involving up to ninety volunteers. Another trial, which plans to reinfect around sixty volunteers who have already been infected with the virus, was approved earlier this week and will soon begin at the University of Oxford.

With global COVID-19 cases hitting an all-time high and over ten thousand people dying daily, the data from these human challenge trials have massive potential to curb the pandemic. Since they take place in extremely controlled conditions, these studies can reveal data about the mechanisms of infection and the body’s immune response from the exact moment of exposure, which is impossible in conventional studies. They can also enable faster vaccines studies to test easy-to-deploy next-generation vaccines against virus variants. My home continent of Africa has been outbid for vaccines by the rest of the world, so developing more vaccines is essential for our recovery. I signed up as a prospective volunteer for challenge studies, so naturally, I celebrated the approval of challenge trials with many other volunteers and advocates. 

International volunteers should be eligible for UK challenge trials

Researchers may face a significant hurdle before they make the most of human challenge studies: getting a sufficiently large and diverse group of volunteers.

To be sure, the amount of willing and altruistic volunteers from all around the world is not in itself a hurdle: nearly 40,000 people from nearly 200 countries have registered their interest with 1Day Sooner, a non-profit where I serve as Africa Chapter Manager. But current challenge trial registration is restricted to the British only, and as vaccination campaigns pick up, the number of eligible volunteers— those who are based in the UK, unvaccinated, extremely healthy, between the ages of 18 and 30, and capable of joining a quarantine facility for three weeks— may quickly dwindle.

Accepting volunteers from around the world— not just Britain— could present a solution to this problem. Thousands of volunteers from Brazil, Africa, and Southeast Asia have signed up as potential volunteers for challenge trials, and given the societal value of these trials, funders should not hesitate to accommodate these volunteers’ travel expenses for the trial. There is no prima facie reason why non-British volunteers like myself would be any less suitable to participate in a COVID-19 challenge trials, so long as the studies themselves are conducted in accordance with the highest possible ethical standards, including a robust informed consent procedure.

The importance of diversity

Including volunteers from around the world can also help ensure trial diversity. Some have argued that trials should exclude Black, Asian, and minority ethnic (BAME) volunteers on grounds that such volunteers are at greater risk from the coronavirus, but this would be a grave error. So long as they are sufficiently young and healthy, volunteers from around the world should be allowed to take part in the UK’s Human Challenge Programme.

Data do show that BAME populations are at higher risk of severe illness and death from COVID-19. However, when the average risk is disaggregated to account for age, sex, race, co-morbidities, and other relevant characteristics, the difference in risk becomes unexceptional. For example, a 22-year-old Black woman has a lower risk from COVID-19 than a 29 year old white man with an identical background. Minimizing risk to trial volunteers must remain the goal, but the data support using multi-factor risk analysis for each volunteer, not a blanket race-based exclusion, which would be arbitrary and unscientific.

Diversity is also essential for the data generated in COVID-19 challenge studies. One of the most basic principles in biostatistics is that samples must be truly representative of the population to which the results are to be applied. Dr. Ubaka Ogbogu, Assistant Professor in the faculty of Health Law at the University of Alberta, has said that “giving people vaccines that they were not involved in during the trials is like testing on them.” Vaccines are being distributed globally, so it only makes sense to allow international volunteers to participate. It is similarly imperative for researchers to prioritize diversity in safety trials and Phase III trials that may accompany challenge studies.


The UK has outstanding capacity and initiative to conduct COVID-19 human challenge trials, and these trials should not be held back by a lack of volunteers when thousands around the world— myself included— are willing to participate. A truly diverse group for a study with global applications would be one with volunteers from around the world, including volunteers in Africa, Brazil, continental Europe, and Southeast Asia.


Author: Zacharia Kafuko

Affiliations: Africa Chapter Manager, 1Day Sooner

Competing interests: ZK works for 1Day Sooner, a non-profit advocating for COVID-19 challenge trial volunteers

Social media accounts of post author: @DeZacliff

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