The United Kingdom government has launched a study that will track the spread of novel coronavirus in the general population, and attempt to discern how long antibodies remain in the blood and if immunity might wear off over time.

Immunity remains one of the major unanswered questions about novel coronavirus. Scientists still do not know if recovery from infection leads to immunity, or if people can become infected a second time.

Some governments have suggested that if people test positive for antibodies, then they could be issued with "immunity passports", enabling them travel or to return to work. Such a system would only be valid if immunity to novel coronavirus is proven, and the World Health Organization says there is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection.

The UK study will aim to determine what proportion of the population has been infected and how long antibodies remain in the immune system, helping scientists gain insight into the immunity question and guiding the UK's management of the pandemic.

Up to 20,000 people of all ages will take part for at least six months, with early data from the study due to be shared in late June.

People in the study will provide a monthly blood sample, which will then be screened for antibodies using a test developed by researchers at the University of Oxford. Participants will also complete a questionnaire about symptoms they may have experienced.

Participants will be drawn from an existing group of 500,000 volunteers that are signed up to UK Biobank, which is a long-term study that is investigating the link between disease and certain genetic and environmental factors. UK Biobank volunteers are aged between 40 and 69, and the COVID-19 study will be open to their children and grandchildren in order to broaden the dataset.

UK Health Secretary Matt Hancock said information gathered will help inform future government strategy, including lockdown and social distancing measures.

"This UK Biobank study will build our understanding of the rate of COVID-19 infection in the general population and, importantly, it will add to our knowledge about the risk factors that mean the virus can affect individuals differently," Hancock said.

Rory Collins, principal investigator at UK Biobank, said the study might help determine how long people remain immune from further infection following exposure to the virus.

"We believe most people have mild or no symptoms of infection with coronavirus, but a small proportion fall very ill," Collins said. "Much better understanding of what proportion of the population has been infected, how long antibodies to coronavirus stay in the blood, and whether immunity wears off, are vital to managing this pandemic."

Two other large novel coronavirus surveillance testing surveys are ongoing in the UK. Imperial College London and market research company Ipsos Mori launched a program in April that uses swabs to understand the level of active infection in participants.

Public Health England is also analyzing blood samples to help detect past and current rates of infection as well as any changes in the virus.