At least 30 per cent of Britons have caught Covid since the pandemic began yet the true toll will always remain a mystery, experts say.
Only 8million people — 12 per cent of the UK’s population — have officially tested positive for coronavirus. Rates are as high as a fifth in the worst-hit towns.
But the actual number will be drastically higher and the Government’s top scientific advisers are ‘actively looking’ for an accurate ballpark figure.
Millions of people who were infected during Britain’s first wave last spring are not included in No10’s official count because they were never able to get tested.
The figure is also skewed by the swathes of the country who caught the virus but never showed any symptoms to get swabbed. And not everyone who gets ill develops one of the three symptoms that warrant a free PCR test — a cough, fever or lack of taste and smell.
Scientists also say it’s impossible to tell the true toll through surveillance studies that specifically look at antibody rates among the population because the virus-fighting proteins — made in response to both natural infection and vaccines — can wane to undetectable levels.
Despite the challenges in estimating a figure, one of the country’s top experts believes around 30 per cent of the country, or 16.8million people, will have caught the virus since it first hit England.
Professor Paul Hunter, an infectious disease expert at the University of East Anglia, told MailOnline estimating how many people have had the virus is ‘not an easy question’.
He added: ‘The big question, however, is what proportion of people who’ve not been vaccinated have already had the virus and so can be considered to be protected.’
Millions of people who were infected during Britain’s first wave last spring are not included in No10’s official count because they were never able to get tested. Graph shows: The five areas of the UK with the most and least positive tests since the start of the pandemic
Professor Paul Hunter (left), an infectious disease expert at the University of East Anglia, told MailOnline he estimates around 30 per cent of people have had Covid. Professor Graham Medley (right), chair of an influential subgroup of SAGE, told MailOnline experts have not yet landed on an exact estimate for all age groups due to difficulties with accounting for asymptomatic spread and waning antibodies but Government scientists are ‘actively looking for one’
Eight million people — 12 per cent of the UK’s population — have officially tested positive for coronavirus. Rates are as high as a fifth in the worst-hit towns
His estimate is based on comparing officially reported cases — published by the Department of Health every day — against modelled estimates taken from a random surveillance scheme that swab tens of thousands of people weekly.
Professor Hunter’s analysis suggests England has picked up around 45 per cent of all modelled cases. This means there would have been around 30 infections for every 100 people, according to his calculations.
He said: ‘But during the first three months of the epidemic we were pretty rubbish at detecting infections that did not lead to severe disease, so that probably makes it closer to 35.’
But Professor Hunter argued the 35 per cent isn’t entirely accurate in determining the proportion of the population that have ever had Covid.
The modelled estimates, which come from the Office for National Statistics, can include the same person testing positive twice over the course of their original bout of the illness — whereas the Department of Health figures are based on individuals.
This means some of the 35 per cent would be counting the same person twice, with a more accurate figure being around the 30 per cent mark.
Professor Graham Medley, chair of an influential subgroup of SAGE, told MailOnline experts have not yet landed on an exact estimate for all age groups due to difficulties with accounting for asymptomatic spread and waning antibodies but Government scientists are ‘actively looking for one’.
Experts at the UK Health Security Agency, which took over the pandemic responsibilities of the now-defunct PHE, carry out regular blood testing to try to answer the question.
UK Health Security Agency experts found around 19 per cent of blood donors over the age of 17 have antibodies produced specifically after being infected with the virus (shown by the red line)
Some 28 per cent of people aged 17 to 29 are likely to have had the virus as of September 12, according to the data — the highest proportion of any age group. Graph shows: The proportion of people with antibodies specific to natural infection (triangle, dotted line) in different age groups versus the proportion with antibodies that can come from infection or vaccination (circle, straight line)
In those aged 70 to 84, just over five per cent (3.7million) tested positive for the antibodies. Graph shows: The proportion of people with antibodies specific to natural infection (triangle, dotted line) in different age groups versus the proportion with antibodies that can come from infection or vaccination (circle, straight line)
Data in the body’s weekly surveillance report, released yesterday, showed around 19 per cent of blood donors over the age of 17 have antibodies that are only produced by the body following a natural infection, meaning the tally is not skewed by vaccines.
Professor Medley said the figure likely underestimates the number of people who have been infected because the antibodies tend to wane within months of infection.
Not everyone produces antibodies and some only do to levels that are not detectable by tests used by UKHSA.
Some 28 per cent of people aged 17 to 29 are likely to have had the virus as of September 12, according to the data — the highest proportion of any age group. In those aged 70 to 84, just over five per cent (3.7million) tested positive for the antibodies.
Professor Hunter said: ‘The problem with antibody studies is that a substantial minority of people do not develop antibodies after a natural infection and even if they do, such antibodies decline.
‘So anybody with a N assay (the test UKHSA uses) antibody positive result has had an infection — but you cannot say that if they are N assay antibody negative that they have not.
‘About 29 per cent of people do not develop antibodies and that is quite a bit higher in asymptomatic people and of course younger people/children are rather more likely to be asymptomatic.’
Nearly a fifth of people in Blackburn have tested positive for Covid since the pandemic began, official figures show. Map shows: The proportion of people who have tested positive in each local authority in the UK
He added: ‘People start losing antibody loosing within a few weeks. So N assay antibody levels do underestimate past infections probably by about a half or so.’
It comes after MailOnline this week revealed nearly a fifth of people in Blackburn have tested positive for Covid since the pandemic began.
The Lancashire authority has been the worst hit area in the UK, recording 12 times more cases per population size than the least affected parts of the UK.
Department of Health data shows around 19,000 per 100,000 people in Blackburn have had the virus since March 2020, compared to just 1,500 in the Orkney Islands in Scotland. Burnley is the second worst affected region, with the virus infecting just under 18 per cent of people.
Covid was least prevalent in remote island and coastal areas of Scotland, Wales and England. After the Orkney Islands, the Shetland Islands — the northernmost part of the UK — had the next lowest case rate, with 2.9 per cent of people testing positive.
More broadly, the figures highlight how northern parts of England — which are typically the most deprived — have borne the brunt of the crisis.
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