THOUSANDS of coronavirus infections are "being missed" because the symptoms criteria used for testing is too narrow.
Professor Mark Woolhouse, an infectious disease epidemiologist at Edinburgh University and member of the Scottish Government's Covid-19 advisory group, said there was a "persistent problem" in Scotland and the rest of the UK that cases were going undetected.
Speaking at an online conference hosted by the Royal College of Physicians Edinburgh, Prof Woolhouse pointed to data showing confirmed cases running at around 2000 per day in Scotland in January at a time when community surveillance by the Office for National Statistics estimated the incidence at 4-5000 per day, and pandemic modelling by UK SAGE (Scientific Advisory Group for Emergencies) put it as high as 11,000 per day.
"What those numbers imply is that we are consistently underestimating in Scotland the size of our epidemic, in terms of case numbers, by roughly 50-60%," said Prof Woolhouse.
"That's quite a large disparity and it's a problem, because if we're not picking up those cases we can't be sure that they are self-isolating, and they're certainly not having their contact traced and those contacts asked to self-isolate.
"It's handicapping our ability to control the spread of infection, and that then has to be picked up by other measures such as social distancing and lockdown."
Prof Woolhouse added that the conventional list of symptoms whereby people are told to self-isolate and seek a test - fever, persistent cough, loss or change in taste or smell - "only account for around half of the cases".
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He said a combination of mass testing and expanding the symptoms criteria would help to counteract the problem, adding that the latter alone could capture an estimated half of the current "missed" cases.
The number of confirmed Covid cases identified in Scotland during the past seven days has fallen to 1878, down 20 per cent week on week and in line with levels last seen in mid-September.
Nonetheless, Prof Woolhouse said the new Kent variant has been "very difficult to suppress" compared to previous forms of the virus and said the country should "be prepared for some kind of third wave this winter", albeit with "hopefully" fewer deaths and hospitalisations as a result of vaccination.
The conference was seeking views from experts on the lessons from the pandemic.
Prof Woolhouse said not enough had been done to protect the most vulnerable.
He highlighted research from Oxford University which found that the top 5% of people most at risk from Covid - based on a combination of age, ethnicity, obesity, poverty and a range of underlying health conditions - accounted for 76% of virus deaths during the first wave, with the 20% most at risk accounting for 94% of the deaths.
"The distribution of mortality is extremely unequal," said Prof Woolhouse, adding that Edinburgh University research has found that a larger proportion of fatal infections during the first wave occurred after lockdown than before.
"We estimate that somewhere up to three quarters of fatal infections occurred after lockdown was imposed.
"What I conclude from that is that lockdown, whatever it did to reduce the transmission and save lives in Scotland, failed to protect a very large number of very vulnerable people.
"One source of those infections were visits to hospital. People who spent periods in hospital during lockdown were particularly prone to suffering severe infections.
"[The researchers] estimate that at least half of those infections may have been from that source, so that's an obvious place where more could have been done to protect vulnerable people."
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Dr Nicholas Phin, director of public health science at Public Health Scotland, said the pandemic "has highlighted the need for inequalities in Scotland to be addressed".
"Unless this takes place then you will see a disproportionate burden of disease in certain sectors of the population."
He also revealed that staycation trips to Blackpool between September an early November were responsible for importing 747 cases to Scotland - around 2% of the total during that period.
David Nabarro, special envoy on Covid-19 at the World Health Organisation, stressed the pandemic was "nowhere near finished" and new variants are "inevitable".
"I have to stress that I'm not 100% sure that world is going to find it easy to vaccinate itself out of this pandemic," he said, noting that only three of the eight vaccines currently in use around the globe - including the AstraZeneca and Pfizer vaccines - have had their clinical trials' data submitted by manufacturers to the WHO.
This is necessary before they can be distributed by the WHO's Covax programme which supplies Covid vaccines to poorer nations.
"In just about every part of the world we're seeing surges," said Mr Nabarro, adding that genomic sequencing is crucial to identifying new strains of the virus early.
"There will be a regular arrival of new variants that are particularly troublesome - that variant problem is going to go on, and on, and on as long as we've got the virus around. It's inevitable.
"In parts of the world where there are large numbers of people infected, we'll go on seeing new variants that are capable to a greater and lesser extent of escaping from the protection of the vaccine
"And as much as countries try to stop new variants coming across their borders, that is a short-term measure."
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