PARTS of London and New York could already have coronavirus herd immunity, scientists claim.
They say as little as 10 per cent of people may need to be infected for the virus to fizzle out.
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Experts previously believed 60 to 70 per cent of the population would need test positive for Covid-19 to gain herd immunity status.
But they now claim between 10 and 43 per cent could be enough to stop the spread of the virus, should a second wave hit.
Scientists at the Liverpool School of Tropical Medicine and the University of Strathclyde found England – as well as Portugal and Spain – to have herd immunity in the range of 10 to 20 per cent.
Data from Imperial College London revealed that six per cent of England's population had already been infected with the virus by July 13.
It means around 3.4 million people in the country could have had Covid-19 – far greater than the UK's official tally of 320,286.
Londoners were most likely to have been infected, with results suggesting that 13 per cent of people in the capital had antibodies.
This compared to less than three per cent in the South West of England.
People from the BAME (black, Asian and other minority ethnic groups) community and healthcare workers were also more likely to have been infected.
And older generations, those with underlying health conditions and people living in larger households were also more at risk.
Antibody testing in New York City suggests that as many as one in five people have had coronavirus.
And a study by researchers at the University of Sussex indicates more than 40 per cent may be immune.
Professor Peter Krüger, a physicist and data scientist at the University of Sussex, told Newsweek that the infection rate will be much higher in some groups, such as key workers, and lower in others.
But he said: "On average, for the whole of New York, it's 40 percent."
The study also showed that deaths after the initial peak fell faster in badly affected cities, compared with regional areas.
Krüger said the fast decline means immunity in a population "was having an effect independent of lockdown measures".
Professor Sunetra Gupta, a theoretical epidemiologist at Oxford University, also believes London and New York may have already reached herd immunity.
Her controversial study claimed that half of the UK population could have had Covid-19, and therefore be resistant to the virus.
Carl Bergstrom, an infectious disease expert at the University of Washington in Seattle, told the New York Times: "Mathematically, it's certainly possible to have herd immunity at these very, very low levels."
And Bill Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, said: "I'm quite prepared to believe that there are pockets in New York City and London which have substantial immunity."
But some experts have cast doubts over herd immunity claims.
Professor John Edmunds, of the London School of Hygiene & Tropical Medicine, said: "The authors suggest that significant numbers of people in London, Madrid and New York may be immune.
"There is, however, a much more direct and reliable way to estimate the levels of immunity in populations.
"That is by taking a representative sample of the population and testing for specific antibodies against SARS-CoV-2 (the virus that causes Covid-19) in their blood."
And Matt Keeling, professor of Populations and Disease, University of Warwick, said he was "sceptical".
He added: "While we would all like to believe that we are past the worst of this outbreak, the rising cases across many European countries would indicate that we are far from herd immunity and measures need to remain in force if we are to prevent a second wave even worse that the first."
The World Health Organization today warned the world is "nowhere near" achieving herd immunity and it is "not a solution we should be looking to".
There is no evidence to suggest that having antibodies present in the system means you cannot be infected by the coronavirus again.
And it is unknown how long antibodies last, with some scientists suggesting they decline three months after infection.
Graham Cooke, research professor of infectious diseases and research lead at Imperial College London, said: "We don't know enough about what antibodies mean in terms of protection so we can't assume that people who've got antibodies are protected, and if they are we don't know how long it would be for."
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