Researchers in England are deliberately exposing volunteers to the coronavirus that causes COVID-19. The aim is to accelerate the development of new vaccines and treatments.

But exposing people to a life-threatening disease without particularly effective treatment seems unnecessary, if not unethical.

Human provocation experiences differ from other COVID-19 studies in one very important respect. “The main difference is control,” says Christopher Chiu, an infectious disease researcher at Imperial College London and lead scientist on the challenge study.

He says that with a challenge study, you know exactly when a person has been exposed to the virus and how much of the virus they have been exposed to.

Without knowing these things, you have to wait until people are accidentally exposed to the virus.

“You will end up having to recruit a lot more people, give a lot more people your candidate vaccine, before you see a result,” Chiu said.

Indeed, it took many months and tens of thousands of volunteers to prove that the Pfizer, Moderna and Johnson & Johnson vaccines worked. A challenge study might, in theory, have been able to show this with a fraction of that number and in much less time.

But that means exposing perfectly healthy people to a dangerous virus.

Chiu says he and his colleagues are well aware of this risk, and that’s why they plan to only include certain types of people in their studies.

“We have known for over a year of a pandemic now that healthy young adults are at very low risk of contracting severe COVID,” he said.

Chiu says that in addition to involving only healthy young adults, the experiments will be conducted at the Royal Free Hospital in London, a facility with extensive experience in caring for COVID-19 patients. Volunteers will be treated at the first sign of illness, a time when therapies seem to be most effective.

But studying only young adults is one of the flaws people see in provocation studies to test the effectiveness of an experimental vaccine, for example.

“The data you get from a challenge study to find out if it works isn’t really going to give you the information you want,” says Seema Shah, lawyer and medical ethicist at Northwestern University Feinberg School of Medicine.

Shah says it’s important to know whether a vaccine works in the elderly, people with poor health, or people of different ethnicities. You don’t get this information from a challenge study.

“When it all started at the start of the pandemic, there was a big reason to do these provocation studies, and that was to speed up vaccine testing,” Shah said.

But now, several COVID-19 vaccines have been shown to work, so the initial momentum has passed.

Another problem facing studies is viral variants. Researchers are expected to collect new baseline data, such as the minimum infectious dose for each new viral variant they want to study, a process that takes time. Still, such studies can be useful for testing vaccines in the future.

For example, if coronavirus cases become less frequent, it will take far more than 30,000 or 40,000 volunteers to say whether a new vaccine is significantly better than those currently available. And it will make it much easier to compare vaccines face to face.

“So under these circumstances, a model of human infection could be very useful,” says Kanta Subbarao, virologist and director of the World Health Organization’s Collaborating Center for Influenza Reference and Research in Melbourne, in Australia.

But she fears that not enough is known about the risks of exposure to SARS-CoV-2, the virus that causes COVID-19, even for healthy young adults.

“We discussed very early on whether we should even consider SARS-CoV-2 and said we wouldn’t,” Subbarao said. “But we are exploring one of the most common cold coronaviruses.”

She believes the work could provide clues to a universal coronavirus vaccine, a vaccine that would prevent both COVID-19 and the common cold.

Right now, Chiu from Imperial College and her colleagues are trying to figure out the minimum amount of virus needed to make someone sick with COVID-19. After that, they can turn their attention to testing new treatments and vaccines.

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