More than one in five Britons (20%) may have already overcome the coronavirus, research suggests.
Since the outbreak emerged at the end of 2019, experts have questioned its prevalance.
A lack of testing at the start of the pandemic means many earlier cases went unreported. While swabs are now in high supply, up to a third of patients are said to develop no symptoms, leaving them unaware they should get tested.
To better understand the coronavirus' prevalance, scientists from the University of Texas Southwestern Medical Center developed a computer model that estimates the number of daily infections in the world's 50 worst-affected countries.
The UK has the highest death toll in Europe, with more than 112,000 confirmed fatalities.
The Texan team's results suggest more than 20% of British residents have already been infected, a "severe undercounting" on the official tally.
Since the outbreak was identified, the UK has officially recorded just under 3.95 million cases, translating as 5.9% of its 66.6 million residents being infected.
Daily coronavirus counts help officials gauge the spread of the infection, guiding the regulations in place to control the virus.
Feeling "substantial undocumented infections have obscured" the true scope of the pandemic, the Texan scientists developed a model that uses machine-learning to estimate the true number of daily infections across the worst-affected countries and all 50 US states.
The model drew on "previously published pandemic parameters, and publicly available daily data on confirmed cases and deaths".
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The results, published in the journal PLOS ONE, suggest "severe under-ascertainment of COVID-19 [the disease caused by the coronavirus] cases" is "universal".
In nine of the countries, the "actual cumulative cases" were estimated to be at least five times higher than the confirmed incidences.
In the UK, US and Belgium, the results suggest more than 20% of the total population has been infected.
As many as 82% of people may need to have overcome the coronavirus, or be vaccinated against it, to achieve herd immunity. This occurs when a sufficient number of people are immune to an infection to prevent it taking hold in a community.
More than 12.2 million people in the UK have had their first coronavirus vaccine dose, while over 512,000 have had the second jab.
In certain US states – like Pennsylvania, Arizona and Florida—more than 5% of people had an active coronavirus infection on 31 January, the Texan results suggest.
In contrast, 1% of people in Washington were infected on that day.
The scientists hope estimating coronavirus case numbers within communities will "help inform contact-tracing and other public health efforts".
"Given the confirmed cases only capture the tip of the iceberg in the middle of the pandemic, the estimated sizes of current infections in this study provide crucial information to determine the regional severity of COVID-19 that can be misguided by the confirmed cases," they wrote.
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