The Department of Health and Social Care has launched its most significant coronavirus study to date with the ambition of testing up to 300,000 people across the country. The aim is twin-fold: to find out how many people currently have the SARS-Cov-2 virus and how many have developed immunity against it.

The scale of the enterprise represents a new development in the government’s strategy to include the general public in widespread “surveillance testing.” Up to the present, testing has been focused on those who are ill in hospitals and among frontline health and social care staff.

The authorities believe extending the testing to the wider public will be essential in helping  the government and the UK’s scientific experts develop new policies to combat the UK’s epidemic when the results become available in early May. But some experts warn that the study will only fulfil its potential if the UK is able to scale up antibody testing. At the moment, the majority of the study will be based on tests for the presence of the virus itself.

The study will be led by a grand alliance of the DHSC and the Office for National Statistics, but it will also draw on the expertise and resources of scientists from the University of Oxford, the data science company IQVIA UK, and the National Biosample Centre in Milton Keynes.

A total of 25,000 households are being contacted to take part in the first, “pilot phase” of a new project to monitor how far Covid-19 has spread. The plan will then be to expand on this initial study over the next twelve months.

The project, if it can reach its eventual target, is vast in its scale and ambitious in its objectives. The DHSC has selected what it believes to be a “representative sample of the entire UK population by age and geography”.

The sample size, the DHSC believe, will begin to provide a rough idea of how many people in the UK have had the virus and detect those who are still vulnerable. The information provided could be used to improve epidemic modelling, and help the authorities decide whether and when Britain could begin emerging from its national lockdown.

The programme will make use of two different types of test. It is understood that the majority of tests will be PCR tests. These detect the presence of the virus from a swab, which can be taken either from the nasal passage or the respiratory tract. All 25,000 people in the first phase of the study will provide swabs for this test.

A smaller number of antibody tests, detecting immunity to the SARS-CoV-2 virus among those who have already had it in the past, will also be carried out. These will use blood samples which are then tested in labs using a process known as ELISA. About 1,000 households will be asked to provide these blood samples, a fraction of the total taking part in the study.

The households in the study will be tested multiple times over the course of the year, initially weekly, and then monthly, regardless of whether they show symptoms or not.

Professor Babak Javid, Consultant in infectious diseases at Cambridge University Hospitals says that this is a good sign. He says: “This will overcome potential biases in testing only those with symptoms, and, since multiple tests will be performed, will also, to an extent, overcome limitations of the test itself, which we know sometimes generates a “false negative”.

But there are concerns among experts that 1,000 households alone will be too small a sample size to provide a useful insight into the number of those who have developed immunity.

Keith Neal, Emeritus Professor in the Epidemiology of Infectious Diseases at the University of Nottingham, urges caution. He warns that “Only including 1000 households in the antibody blood test section is probably too small as this is only 100 per region and we know there are regional variations in the disease. A figure of at least 10,000 tests per region is probably required to get an accurate estimate of the spread that has already occurred.”

Neal urges policymakers that “The sooner it is increased to full scale (to 300,000) the better so we can get the high quality information needed.”

If the UK can expand upon the initial phase of the study, experts say, there is every chance that this will be a vital tool in combatting Covid-19. Lawrence Young, Professor of Molecular Oncology at Warwick Medical School, explains that knowing more about the extent of immunity “is vital in informing the government on how best to ease the lockdown.”

Young also says it “will help us to better understand how the virus has spread” and “to decide how best to use a vaccine or other interventions – when they become available.”

When it comes to testing in general, the government’s official Covid-19 testing coordinator, Professor John Newton, may also have some good news. Speaking at tonight’s Downing Street press briefing, Newton remains convinced that the UK remains “on track” to reach its goal of 100,000 tests (of all types) per day by the end of April.

“We are currently on track to reach 100,000 tests a day,” he said, adding that he believes “we’re somewhat ahead of where we thought we’d be at this stage.”

Newton revealed tonight that there are 31 drive through testing facilities in operation across the UK, and there are plans to add a further 48 pop-up testing centres in the coming weeks.