UK scientists are planning to reinfect a group of volunteers with COVID-19 in a world-first trial. Researchers from Oxford University say the study will be an important part of working out who is really immune from the virus and for how long.

The UK reported just four COVID-19-related deaths on Monday, the lowest level since early September. But keeping the path out of lockdown clear remains a challenging task. Officials have confirmed that 182 cases of a variant first identified in India have been found in the UK.

Keeping potentially vaccine-resistant strains at bay will be a vital part of the UK strategy. The country's largest surge-testing program to date has been unleashed across several parts of London in recent days, after cases of the mutation first seen in South Africa also emerged.

Among those attending a polymerase chain reaction (PCR) test center in Lambeth on Monday was a man who had already received two doses of a COVID-19 jab. He remains vigilant but worries that others will not, adding that "people in the streets don't use masks."

Officials may want to avoid too many positive headlines for fear of creeping complacency that might undermine the successful effort to suppress the virus. But they keep on coming. On Sunday, crowds returned to the stadium for the FA Cup football semi-final. The few thousand who entered had to show proof of a negative COVID-19 test first. Like surge testing, "immunity certificates" could soon become something of a post-lockdown norm.

There remains much to learn about how to keep people safe amid a gradual return to normality. New trials form part of that effort. The UK is the only country in the world to start carrying out what are known as "human challenge trials" for COVID-19, in which a group of volunteers is infected on purpose. One trial run by Imperial College has already started. A second by Oxford University researchers has also been approved.

Participants, who will be young and healthy, could be paid up to $7,000 for taking part and will be constantly monitored. The ultimate aim is to work out how much virus it takes for people to become sick a second time, which individuals have immunity, and which don't. It will also seek to discover how long such protection lasts.

"If volunteers have a certain level of a particular kind of antibody response before we try to reinject them, we may find it may not be possible to reinfect them," says Oxford professor of Vaccinology Helen McShane, who is also the study's lead researcher. "That tells us that a particular antibody response is sufficient for protection."

A recent U.S. study of a similar demographic found up to 10 percent of people who had caught COVID-19 contracted it twice.

Making people sick on purpose does carry a certain level of risk, while only the original strain first identified in Wuhan, China will be used for now – despite the fact that mutant strains are often more prevalent.

The hope is that these groundbreaking studies will help not just the UK, but the world, eventually bringing this pandemic under control.