At the Centre for Applied Microbiology and Research, housed within the high security Defence Science and Technology Laboratory at Porton Down near Salisbury, scientists are poring over 800 blood samples taken from a representative sample of the English population. They are conducting tests today which, more than any others you may have read about, will decide the shape and timing of Britain’s coronavirus exit strategy. Perhaps, just perhaps, they will provide the key to the door that is lockdown. If the tests work, and virologists are confident they will, they will provide Britain with the answers to the most important unknowns about Covid-19: How many of us have already had the virus? How common are asymptomatic carriers? And how much immunity, if any, do we acquire after surviving an infection? The answers to these questions are what virtually every government the world over is rushing to unearth. They are the gold dust of the pandemic. They will inform not just exit through a much more precise modelling of the pandemic’s trajectory, but the best approach to treatments and vaccines. Little wonder then that this - the “fourth pillar” of the government’s testing strategy - is being conducted behind the high security fences of Porton Down.

The Porton Down facility Credit : TOBY MELVILLE/ REUTERS

“This sort of study is absolutely vital because we are so uncertain about the level of infection in the population”, said Mark Woolhouse Professor of Infectious Disease Epidemiology at the University of Edinburgh. “As things stand we could be out by a factor or 10 or even 100. If work like this gives us even a rough pointer initially it would be hugely valuable”. While some elements of the British response have been slow, the work at Porton Down is understood to have been underway since January. Moreover, it plays to our skill set as a nation, based as it is on high-end science rather than the more mundane - but crucially important business - of high volume throughput or production. Experts say the first two months were spent validating high tech “assays” for reliably identifying coronavirus antibodies and designing a robust longitudinal blood sampling study. The first 800 blood samples were delivered to the laboritary in late February. “We are expanding this programme during April so that we have the potential to test around 5,000 samples per week”, said the Department of Health and Social Care. “We will also roll out a national mass population sample over the coming months... the aim is to enrol 16,000 to 20,000 people who will undergo repeat testing”. Attention has been focused on swab tests for the virus and cheap home antibody tests to tell people if they have already been infected. While the swab tests are reasonably precise, the home antibody testing kits are currently woefully inaccurate.

In contrast, the antibody tests or “assays” being run at Porton Down are said to be excellent. “The tools are there. The expertise is there. You can be quite confident PHE at Porton Down has access to sensitive assays that can accurately determine antibody levels in patients’ blood,” said Zania Stamataki, a senior lecturer in viral immunology at the University of Birmingham. Dr Stamataki added that it was these Porton Down assays that the commercial antibody tests which the government has taken options on are being validated against. The initial aim of the work at Porton Down is to establish how widely the virus has spread. Current models assume the spread to date is fairly modest, at around three to four per cent of the population. If the modelers had a more precise grip on this crucial variable they would be able to predict the course of the epidemic with much greater certainty. “Data in the coming weeks will enable estimation... with greater precision,” the team at Imperial College London, whose work underpins the UK’s lockdown strategy, admit in a report dated March 30. Prof David Heymann, infectious diseases expert at the London School of Hygiene and Tropical Medicine, added: “Community surveys will provide us with idea of the level of people infected and that is very important to inform the modelling. Modelers use best possible data at the time they do the modelling, but this changes rapidly.” Just as a political pollster can take a small but representative sample of the population to establish voting intentions with some accuracy, the scientists at Porton Down hope to pin down a figure for the spread of the virus from the initial 800 blood samples they are currently studying. This will be improved on as they test more blood samples over time.

The study will also provide data on the vexed question of how many people with Covid-19 experience no symptoms or symptoms so mild they carry on as normal and (perhaps) unwittingly spread the disease to others. This again is vital information for those devising Britain’s exit strategy. Current estimates for non-symptomatic carriers vary hugely. “Blood antibody tests themselves will not tell you about symptoms but if you have gathered detailed clinical information from those you are taking blood from it should do”, said Prof Woolhouse. Karol Sikora, professor of medicine at the University of Buckingham and former director of the WHO, added: “In studies on cruise ships and small countries, where they’ve tested just about everyone, some 50 per cent of people infected have no symptoms whatsoever, not even a sore throat or cough. “That number could mean 20 to 30 per cent of the population have been infected in the UK, which would have huge implications for our strategy - especially around herd immunity and NHS capacity. That information really is vital.” Last, and perhaps most important, the work at Porton Down will - over the course of six months to a year - show whether or not the antibodies produced as a result of contracting Covid-19 give protection against the virus, and how long that protection lasts. Currently, science is completely in the dark about this, the single most important question of all.