British researchers on Tuesday said they hope to expose healthy volunteers to the virus that causes Covid-19 in a groundbreaking study to discover the amount needed for people to become infected.

The Human Challenge Programme -- a partnership that includes Imperial College London -- hopes the work will ultimately help to "reduce the spread of the coronavirus, mitigate its impact and reduce deaths".

In what researchers called a world first, the opening stage of the project will examine the possibility of exposing healthy volunteers to the SARS-CoV-2 coronavirus. They aim to recruit volunteers between the ages of 18 and 30 with no underlying health conditions such as heart disease, diabetes or obesity.

"In this initial phase, the aim will be to discover the smallest amount of virus it takes to cause a person to develop Covid-19," Imperial College said in a statement.

The volunteer would be infected via the nose, Peter Openshaw, professor of experimental medicine at Imperial, told BBC Radio 4 on Tuesday.

"The great advantage of these volunteer studies is that we can look at each volunteer very carefully not only during the infection but also prior to infection, and we can work out exactly what's going on at every stage," he added.

The researchers would use the results to study how vaccines might work and to explore potential treatments.

Because the study deliberately infects the volunteers, "it should be possible for scientists to begin to establish efficacy very quickly, by testing if those who have had a vaccine are less likely to become infected with the virus", explained the researchers.

"Our number one priority is the safety of the volunteers," said Chris Chiu, from Imperial's department of infectious disease. "No study is completely risk free, but the Human Challenge Programme partners will be working hard to ensure we make the risks as low as we possibly can."

"The UK's experience and expertise in human challenge trials as well as in wider COVID-19 science will help us tackle the pandemic, benefiting people in the UK and worldwide," he added.

But Jonathan Ball, professor of molecular virology at the University of Nottingham, warned that safety concerns may limit what researchers can learn from the study.

"Any studies involving the novel coronavirus will focus on those most likely to experience a mild infection –- young healthy volunteers," he said in a press release from the Science Media Centre.

"Yet the people we need to protect against serious disease are more vulnerable elderly people, so what we learn from challenge studies might have limited wider relevance."

The study is expected to begin early next year, said the research team from the partnership, which also includes the government, a clinical company and a hospital.