UK will soon expose volunteers to Covid in world’s first ‘human challenge’ study

LONDON — The U.K. is set to be the first country in the world to run a Covid-19 “human challenge” study, following approval from the country’s clinical trials ethics body.

The first Covid-19 human challenge trial will see up to 90 volunteers, aged 18-30, exposed to Covid-19 “in a safe and controlled environment to increase understanding of how the virus affects people,” the British government said in a statement Wednesday.

Researchers are calling on healthy young people, who are at the lowest risk of complications resulting from coronavirus, to volunteer for the study. Volunteers will be compensated for the time they spend in the study, which is set to begin within a month.

The study is being backed by a £33.6 million ($46.6 million) investment from the British government, with the trial being delivered by a partnership between the government’s Vaccines Taskforce, Imperial College London, the Royal Free London NHS Foundation Trust and clinical company hVIVO, which has pioneered viral human challenge models.

How it works

The study will involve establishing the smallest amount of virus needed to cause infection (known as a virus characterization study) with volunteers exposed “in a safe and controlled environment,” the government said.

“The safety of volunteers is paramount, which means this virus characterisation study will initially use the version of the virus that has been circulating in the U.K. since March 2020 and has been shown to be of low risk in young healthy adults,” it added. Medics and scientists will closely monitor the effect of the virus on volunteers and will be on hand to look after them 24 hours a day.

The study will help doctors understand how the immune system reacts to coronavirus and identify factors that influence how the virus is transmitted, including how a person who is infected with Covid-19 transmits infectious virus particles into the environment.

Once the initial study has taken place, participants could be given an approved vaccine and then exposed to the Covid-19 virus to identify the most effective vaccines.


Such trials are not without controversy given that participants are deliberately exposed to pathogens, but they are seen as playing a key role in developing effective vaccines and treatments.

“Over many decades, human challenge studies have been performed safely and have played important roles in accelerating the development of treatments for diseases including malaria, typhoid, cholera, norovirus and flu,” the British government noted.

Guidance from the World Health Organization says that human challenge trials are ethical when they meet certain criteria. Protections should clearly be in place, experts said, including that trial participants are relatively young and in good health and provided with the highest quality medical care with frequent monitoring.

The WHO notes that it is essential challenge trials are “conducted within an ethical framework in which truly informed consent is given” and that they should be undertaken with “abundant forethought, caution, and oversight.” 

Consideration must be given to both potential individual risks and benefits, WHO says, as well as to potential societal benefits and risks, such as the release into the environment of a pathogen that might not otherwise be present.

The U.K.’s human challenge trial will take place in the next few weeks within the Royal Free Hospital’s specialist and secure clinical research facilities in London. These facilities “are specifically designed to contain the virus. Highly trained medics and scientists will be on hand to carefully examine how the virus behaves in the body and to ensure the safety of volunteers.”

Race against variants

The approval for the human challenge trial, from the U.K.’s Ethics Committee, comes in the same week that the U.K. hit its target of offering a first dose of a coronavirus vaccine to 15 million people in its top four priority groups, including health care workers, the elderly and over-70s.

There is an urgency to the vaccine rollout given concerns over the spread of variants of the virus, with one particular strain that emerged in the U.K. late last year now the dominant version in Britain, and detected in over 80 countries worldwide. Nonetheless, so far preliminary studies have shown that the current coronavirus vaccines are still effective against new variants of the virus.

Clive Dix, interim chair of the U.K.’s Vaccines Taskforce, commented that human challenge trials were vital to better understand the virus and efficacy of vaccines.

“We have secured a number of safe and effective vaccines for the U.K., but it is essential that we continue to develop new vaccines and treatments for Covid-19. We expect these studies to offer unique insights into how the virus works and help us understand which promising vaccines offer the best chance of preventing the infection.”

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