Herd immunity is the only long-term solution to Covid-19 but the idea has wrongly become "taboo", a leading scientist has said.

The concept currently "provokes hostility and controversy" but it must be revisited, according to Raj Bhopal, emeritus professor of public health at Edinburgh University.

In a new article published in the journal Public Health in Practice, he argues that the Covid-19 pandemic has put ministers in a "zugwang" - a position in chess where every move is disadvantageous and where every plan must be examined "however unpalatable" it might be.

Herd immunity is when enough people become resistant to a disease - through vaccination or previous exposure - that it can no longer significantly spread among the rest of the population.

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With no vaccine available for Covid-19, herd immunity relies on enough people in the population becoming infected to lessen the impact of the disease.

Bhopal argues even if a vaccine is found it may not work well for older people and those with underlying health conditions.

The side-effects from a vaccine might also be worse for children and young people's health than catching coronavirus in the first place.

"Herd immunity provokes hostility and controversy as it is usually interpreted as allowing the pandemic to unfold without interventions. The concept needs revisiting," his paper says.

"If safe and effective vaccines and life-saving preventative and therapeutic medications are not found, lengthy lockdowns prove impossible, and the pandemic does not disappear spontaneously, population immunity is the only, long-term solution."

Bhopal, who has advised the government on public health issues, said the 40-50 per cent infection rate needed to achieve herd immunity could be reached by allowing Covid-19 to spread among young and healthy people.

"Allowing infection in those at very low risk while making it safer for them and wider society needs consideration but is currently taboo," his paper says.

Bhopal told The Daily Telegraph: "Why do we not like herd immunity? Discussion of it has been closed down because people equate it with letting the pandemic rip through a population without any control measures at all.

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"I am completely against that, it would be insane. I am not advocating that we dispense with all control measures, we still need to wash our hands, keep our distance and do everything we are being advised to.

"The bottom line is that older people have got a lot to gain from lockdowns and a lot to lose from the infection. Young people have a lot to lose from lockdowns and not much to lose from the infection.

The concept of herd immunity is controversial. Photo / 123rf
The concept of herd immunity is controversial. Photo / 123rf

"Our efforts should be directed towards protecting people who are at high risk."

The concept of herd immunity prompted a backlash when it was first mentioned by the UK's chief scientific adviser in March.

Sir Patrick Vallance said at the time a degree of herd immunity would help the UK population as Covid-19 spread.

He explained the aim was to "reduce the peak, broaden the peak, not suppress it completely".

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Also, because the vast majority of people get a mild illness, "to build up some kind of herd immunity so more people are immune to this disease and we reduce the transmission".

Around 60 per cent of Britain's population would need to contract coronavirus in order for herd immunity to stave off the disease in future, he added.

However, the government quickly moved to distance itself from his remarks. Health Secretary Matt Hancock insisting herd immunity is a "scientific concept, not a goal or a strategy".

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Earlier this month, an Oxford University study suggested the UK might have already achieved a sufficient level of herd immunity to stop a second wave of coronavirus.

Scientists said the "threshold" of herd immunity might have been lowered because many people might already be immune to the disease without having caught it.

According to a new model produced by an Oxford University team led by Professor Sunetra Gupta, as little as 20 per cent of the population may need to be resistant to the virus in order to prevent a new epidemic spreading.

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However, Sussex University researchers have warned predictions herd immunity can be reached when fewer than 40 per cent of the population have been infected are "optimistic" and cannot be relied on.

Professor Istvan Kiss, from the university's School of Mathematical and Physical Sciences, said such predictions could lull people into a "false sense of security" at a time when Covid-19 still poses a "great risk" to society.