Adopting such strategies would not end the pandemic but rather result in recurring epidemics, according to an open letter signed by 80 international researchers published by The Lancet.
The authors argue that any strategy relying on immunity from natural infections of coronavirus is “flawed”, adding that uncontrolled transmission in younger people risks ill-health and death across a whole population.
Instead, the letter, referred to by its authors as the John Snow Memorandum, calls for suppression of the virus until there is an effective vaccine.
It comes after Health Secretary Matt Hancock dismissed herd immunity as “flawed” without a vaccine, telling the Commons it was “simply not possible” to segregate the old and the vulnerable.
The letter’s authors acknowledge that lockdowns have had a substantial effect on mental and physical health and harmed the economy, leading to “widespread demoralisation and diminishing trust” among communities.
The letter says: “The arrival of a second wave and the realisation of the challenges ahead has led to renewed interest in a so-called herd immunity approach, which suggests allowing a large uncontrolled outbreak in the low-risk population while protecting the vulnerable.
“Proponents suggest this would lead to the development of infection-acquired population immunity in the low-risk population, which will eventually protect the vulnerable.
“This is a dangerous fallacy unsupported by scientific evidence.”
The authors warn there is no evidence for lasting protective immunity after natural infection, and so the strategy could result in repeated waves of transmission over several years.
This would put vulnerable populations at risk for the “indefinite future”, as it would not end the Covid-19 pandemic but result in recurrent epidemics, they add.
The researchers argue that defining who is vulnerable would be “complex”, while prolonged isolation of large swathes of a population is “practically impossible and highly unethical”.
Additionally, the authors say it is still not understood who might suffer from long Covid – when people experience symptoms months after infection.
“The evidence is very clear: controlling community spread of Covid-19 is the best way to protect our societies and economies until safe and effective vaccines and therapeutics arrive within the coming months,” the letter concludes.
“We cannot afford distractions that undermine an effective response; it is essential that we act urgently based on the evidence.”
Speaking in the Commons on Tuesday, Mr Hancock criticised the so-called Great Barrington Declaration, which calls for an easing of lockdown measures in a switch of strategy to a herd immunity approach.
Mr Hancock said: “It says that if enough people get Covid, we will reach herd immunity. This is not true.
“Many infectious diseases never reach herd immunity, like measles and malaria and Aids and flu, and with increasing evidence of reinfection, we should have no confidence that we would ever reach herd immunity to Covid, even if everyone caught it.
“Herd immunity is a flawed goal without a vaccine, even if we could get to it, which we can’t.”