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A study from King’s College London revealed that one in five people in London and the South East who have had coronavirus did not show any symptoms after undergoing antibody testing. Antibody tests are used to see whether a person has the protective proteins produced to help fight off the virus, providing any long-lasting immunity to coronavirus.
The study also found that more than a quarter (27 percent) of people who did fall ill did not display the three main signs of COVID-19 – persistent cough, fever and loss of smell (anosmia).
Researchers said this is the first UK-based pre-print study linking detailed ongoing symptom collection data with antibody testing and highlights the likely extent of COVID-19 infection across the region.
Professor Tim Spector, from King’s College London, said: “These results suggest that both swab and antibody testing significantly under-estimate the extent of coronavirus infections in the population.
“We need to combine testing approaches together with getting as many people as possible logging their daily health through the COVID Symptom Study app to really understand the spread of the virus and control it over the months ahead.”
The King’s College London researchers carried out antibody testing on blood samples from 432 adults aged 18-89 in the ongoing TwinsUK study living in Greater London and south-east England.
Of those, 382 had also been regularly logging their health over three months using the COVID Symptom Study app.
Participants were tested for coronavirus to check whether they were currently infected and asked if they had ever previously been tested.
Researchers found that one in eight (12 percent) were positive for viral antibodies.
Focusing on 48 people with a positive antibody result who had also been regularly logging their health, the researchers found that nearly one in five (19 percent) never experienced any symptoms throughout the duration of the study.
More than one in four (27 percent) with antibodies and experienced symptoms did not have the three core NHS symptoms.
However, the non-peer-reviewed study found that loss of smell alone was still highly specific for having the virus, compared with the combination of all three symptoms.
The scientists said this highlights its importance as a key early warning sign of the disease.
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Around half of the app users who reported symptoms which were highly predictive of the disease did not have antibodies against the virus, confirming other studies showing that current antibody testing misses a substantial fraction of cases, researchers said.
Similar results were found by academics at Oxford University which undertook a study of 9,000 people and tested them all for COVID-19 antibodies.
It revealed that large numbers of people were getting negative results despite actually having the virus.
The Oxford University study looked at the results of antibody tests among healthcare workers who claimed that they had lost their sense of taste or smell, a common symptom of COVID-19.
Of the 903 people who tested positive for antibodies following a single test, 47 percent said that they reported a loss of their sense of taste or smell whilst a further 387 people also tested just below the threshold in terms of antibodies for a positive test but did not have symptoms.
However, these test results fell just below the threshold for a positive antibody result, meaning they would not be classed as having the virus.
Several different tests were also used with varying degrees of sensitivity rates.
Dr Tim Walker, from Centre for Tropical Medicine and Global Health at the University of Oxford, told The Sunday Telegraph: “You can see that below the cut-off, there is a rising proportion of people who report a loss of their sense of smell or taste, and this suggests that the test threshold is missing people with mild disease.”
A Department of Health and Social Care spokesperson, said in response: “We do not yet know whether antibodies indicate immunity from reinfection with coronavirus or if they prevent transmission.
“However, antibody testing is an important part of our testing strategy because it helps us understand how COVID-19 is spreading across the country.”
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