- Thirty-six participants, aged 18 to 29, were given a low dose of the original
COVID-19 strain. - Half of the participants became infected, most of whom had mild-to-moderate symptoms.
Scientists conducted the first "human challenge" trial in the UK that involved deliberately exposing 36 people to COVID-19, according to a study preprint currently under scientific review.
In the trial conducted by researchers from Imperial College London and clinical-research organization Open Orphan, healthy male and female volunteers aged 18 to 29 were given a low dose of the original coronavirus strain via nasal drops. They were then monitored for two weeks under quarantine conditions.
Eighteen volunteers eventually became infected, with 16 reporting experiencing mild-to-moderate symptoms, such as runny noses and sore throats. Thirteen of the infected volunteers reported temporarily losing their sense of smell. However, this was restored within 90 days in all but three participants, according to a press release from Imperial College London.
According to the researchers, no serious adverse events were observed among the participants.
The 18 to 29 age group "are believed to be major drivers of the pandemic and these studies, which are representative of mild infection, allow detailed investigation of the factors responsible for infection and pandemic spread," said Chris Chiu, a professor of infectious diseases at Imperial and the trial's chief investigator, in Imperial's press release.
While the trial results have not yet been peer-reviewed, the study could form the basis for future investigations into new treatments for COVID-19. The Imperial researchers say they plan to conduct a similar study using the Delta variant and could start tests using human challenge trials by the end of this year.
In February 2021, Britain became the first country to approve human challenge trials for COVID-19.
Human challenge trials have previously aided in creating vaccines and treatments for diseases such as the flu, typhoid, malaria, and cholera. However, some scientists have questioned whether the results obtained are worth the risks to the studies' participants.
"In my mind, it's still not entirely clear whether these studies are ethically justified, and I'm waiting to see what else they've found," bioethicist Seema Shah of the Lurie Children's Hospital and Northwestern University told the scientific journal Nature.
Vaccine scientist Meagan Deming of the University of Maryland acknowledged that the Imperial study confirmed the insights obtained from other Covid studies. However, she told Nature that she remained concerned about exposing study participants to strains of COVID-19 that had not been weakened.
She also noted the number of participants in the Imperial trial who faced long-lasting problems with their sense of smell or taste, describing this as the "most serious risk that materialized" and "one to keep an eye on."
"This study reads like a promissory note that ultimately, in conjunction with the other research they're doing, there will eventually be substantial scientific and social benefits. But we're not really seeing that yet," Deming said.
But other scientists argue that human challenge studies offer unique benefits.
"Scientifically these studies offer [a] real advantage because the timing of exposure to the virus is always known exactly, therefore things like the interval between exposure and the profile of virus shedding can be accurately described," said Prof. Sir Jonathan Van-Tam, Deputy Chief Medical Officer for England, according to Imperial's press release.
The study "has provided further key data on COVID-19 and how it spreads, which is invaluable in learning more about this novel virus, so we can fine-tune our response," he continued. "Challenge studies could still prove to be important in the future to speed the development of 'next-generation' Covid-19 vaccines and antiviral drugs."