BRITAIN is "miles off" achieving coronavirus herd immunity – and may never reach natural levels of protection, experts have warned.
It comes as a major new study found millions of Brits are still at risk of catching Covid-19 – even if they've already had it.
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Scientists at Imperial College London said immunity is “waning” and noted a 26 per cent drop in positive antibody tests in three months.
In a briefing with journalists, Professor Helen Ward, who worked on the study, said their findings suggest the UK is a "long way" from reaching herd immunity.
She said: "Even at best, (in the first round of the study) 94 per cent of the population remained not likely protected, and now that has declined to over 95 per cent of the population who don't have evidence of antibodies.
"So I think we are a long, long way from any idea that the population will be protected by other people."
We are a long, long way from any idea that the population will be protected by other people
Prof Ward explained: "The way herd immunity works is if you bring an infection into, say a workplace, you don't have much probability of passing it on.
"That can happen with a vaccine or if everybody got infected at the same time.
"But if you think 95 out of 100 are not immune and likely to be susceptible then we are a long, long way from protection.”
Professor Wendy Barclay, also from Imperial, also agreed that Britain is "miles off" achieving natural immunity levels.
She told reporters: "Looking in detail in certain geographical areas, maybe, after intense circulation [we can achieve herd immunity."
"But in terms of waning immunity, it does bring into question whether we can ever achieve herd immunity with this kind of infection [Covid-19].”
Herd immunity was touted as a strategy at the start of Britain's coronavirus outbreak, however, it was quickly denied by the government.
Health Secretary Matt Hancock released a statement on March 15, which said: "We have a plan, based on the expertise of world-leading scientists. Herd immunity is not a part of it."
Sweden’s government opted to use herd immunity as a strategy to beat coronavirus.
Rather than carry out a strict lockdown, it issued numerous guidelines to help people through the coronavirus pandemic such as staying home if they were ill, washing hands and social distancing.
No businesses were forced to shut down, as Sweden wanted to limit the impact on its economy.
What is herd immunity?
Herd immunity refers to where enough people in a population have immunity to an infection to be able to effectively stop that disease from spreading.
Herd immunity is typically best achieved with vaccination.
While the term herd immunity is widely used, it can carry a variety of meanings.
The NHS outlines “herd immunity” as when enough people in a community are vaccinated against a disease, making it more difficult for it to spread to susceptible individuals who have not yet been or cannot be vaccinated.
Academics from the London School of Hygiene and Tropical Medicine wrote that while some use the term to describe the proportion of individuals in a community who are immune to a condition, others use it in reference to “a particular threshold proportion of immune individuals that should lead to a decline in incidence of infection”.
They added: “A common implication of the term is that the risk of infection among susceptible individuals in a population is reduced by the presence and proximity of immune individuals.”
Swedish health experts have claimed they are beating coronavirus because of immunity after refusing to go into lockdown.
WHO's emergencies chief Dr Michael Ryan appeared to quash that theory at a press briefing in August.
He told reporters that we should not live in hope of achieving natural herd immunity.
Dr Ryan said: "As a global population, we are nowhere close to the levels of immunity required to stop this disease transmitting.
"This is not a solution and not a solution we should be looking to."
Meanwhile, the Imperial College team suggest that a coronavirus vaccine could still be effective, despite their findings.
Their study involved more than 365,000 randomly selected adults who tested themselves at home using a finger prick test to check if they had antibodies against Covid-19.
Over this period, the proportion of people who tested positive for antibodies declined by 26.5 per cent, suggesting they reduce in the weeks or months after a person is infected.
Experts leading the Real-Time Assessment of Community Transmission (React-2) study said the findings suggested immunity was "waning quite rapidly", which could lead to an increased risk of reinfection.
However, Professor Barclay said there was still reason to be optimistic about a vaccine being able to stimulate longer-lasting protection.
She told Times Radio today: "I think that we can still continue to be optimistic about vaccines because vaccines will work in a different way.
"What we're measuring at the moment is the way that our bodies' immune response reacts to the virus infecting us.
"But when we immunise with vaccines, particularly the new generation of vaccines that have been developed and put forward into trials for Sars-CoV-2, the virus that causes Covid, they work in quite different ways and they might make an immune response which is much more long lasting than natural infection.
"So we have to keep optimistic about that."
Professor Paul Elliott, director of the React programme and also from Imperial, told BBC Radio 4's Today programme that a vaccine response "may behave differently to the response to natural infection".
Asked what the implications were for a vaccine and how long protection from a vaccine may last, he said: "I think that's an open question that needs to be kept under close research and close scrutiny over the coming weeks and months.
"It's possible that people might need booster vaccines.
"For some viruses there's lifelong immunity, for the coronaviruses that doesn't seem to be the case and we know that you know that that the immunity can fluctuate so, yes, this is something that needs to be looked at very carefully."
VACCINE STILL NEEDED
He said healthcare workers were found to have higher levels of antibodies in the study, as did people living in large households and those from black, Asian and minority ethnic backgrounds.
Professor Graham Cooke from Imperial, who also worked on the study, said: "The big picture is after the first wave, the great majority of the country didn't have evidence of protective immunity.
"The need for a vaccine is still very large, the data doesn't change that."
Eleanor Riley, professor of immunology and infectious disease at the University of Edinburgh, said the study suggested that home antibody testing kits were not useful for people trying to assess their own previous exposure.
She added: "These data should not be taken to infer that a vaccine would only induce short-term immunity.
"Vaccines contain immune stimulators (adjuvants) that induce durable immune responses and the administration of multiple doses of vaccine ensures that high concentrations of antibodies (that decline only slowly over time) are achieved in the majority of vaccine recipients."
Dr Alexander Edwards, associate professor in biomedical technology at the University of Reading, said the rapid home tests used in the study are generally only "able to detect only high levels of antibody".
He said other lab-based tests can detect really low levels of antibodies, adding: "When people are ill, antibody levels rise, and when you heal, antibody levels do drop naturally – this is not exactly the same as losing immunity.
"What is not clear is how quickly antibody levels would rise again if a person encounters the Sars-CoV-2 virus a second time.
"It is possible they will still rapidly respond, and either have a milder illness, or remain protected through immune memory.
"So even if the rapid antibody test is no longer positive, the person may still be protected from re-infection.
"But we don't know this yet, it takes time to work this out, by following large groups over many months, and this type of study is ongoing yet hard and slow."
The React study found that people aged 18 to 24 had the highest prevalence of antibodies and lowest decline in antibody levels, at 14.9 per cent.
Meanwhile, people aged 75 and over had the lowest prevalence and saw the largest drop, with antibody levels falling by 39 per cent.
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