Herd immunity approach to coping with coronavirus would be a ‘dangerous’ error, experts say

Trying to cope with coronavirus by letting it spread to develop herd immunity would be a ‘dangerous’ error with no basis in science, leading experts have warned.

In a letter to the UK’s top medical journal The Lancet, 80 experts on medicine and public health have called for immediate action to stop the disease in its tracks.

Politicians and scientists have for months toyed with the idea of allowing the virus to spread through the population so that people become immune to catching it a second time and it eventually runs out of fuel for outbreaks.

The policy has been used in Sweden, which hasn’t had any coronavirus lockdowns during the pandemic but has suffered a high death toll as a result. 

The Great Barrington Declaration petition launched this month calling for Governments to adopt this approach and claims to have been signed by more than 30,000 medical and health professionals and 450,000 members of the public. 

But Boris Johnson has shot down the idea, this week saying that the number of deaths would be too great to bear if the controversial approach was taken.

Scientists now warn in their letter that to follow the approach suggested by the Great Barrington petition would be a ‘dangerous fallacy unsupported by scientific evidence’. 

They said there is no proof people even get immune after catching the virus once, and that the process of letting it spread would cripple hospitals everywhere.

Health and care workers would face ‘unacceptable’ burdens and trauma in the face of a devastating and uncontrollable pandemic, they said, and it could leave many survivors with poorly-understood and long-lasting side effects known as ‘long Covid’.

Some experts have called for politicians to allow the virus to spread among younger people, for whom it is not as deadly, while protecting the most vulnerable. Scientists say there is no evidence this would work and it may not even be possible (Pictured: A crowds of people in London this month)

‘Uncontrolled transmission in younger people risks significant morbidity [illness] and mortality [death] across the whole population,’ the letter said.

It warned that it would be ‘unfeasible’ to selectively isolate only the people who are most at risk of dying if they catch coronavirus.

People in the most vulnerable categories include the elderly, cancer patients, people with long-term illnesses and potentially black and ethnic minority people in the UK.


Herd immunity occurs when a disease runs out of room and can no longer spread because enough of the population have been exposed to it, either because they’ve already had it or have been vaccinated.

If nobody is immune to an illness – as was the case at the start of the pandemic – it can spread like wildfire. But if, for example, half of people have developed immunity there are only half as many people the illness can spread to.

As more and more people become immune the pathogen finds it harder and harder to spread, until its pool of victims becomes so small it can no longer spread at all.

The threshold for herd immunity is different for various illnesses, depending on how contagious they are – for measles, around 95 per cent of people must be vaccinated to it spreading. For polio, which is less contagious, the threshold is about 80-85 per cent.

But because there is no vaccine for Covid-19, it means actively hunting down herd immunity through natural exposure is controversial because it would mean tens of thousands of people would die.

Government advisors have previously said around 60 per cent of Britain would need to be infected to achieve herd immunity — around 40million people. But, in theory, it would mean around 240,000 Britons would die, given that the SARS-CoV-2 virus is estimated to kill around 0.6 per cent of everyone it infects.

And scientists still do not have any firm proof as to how long immunity actually lasts once a person has fought off Covid-19, and doctors around the world have warned of re-infections — even though the evidence suggests they are less serious.

Some research has suggested the herd immunity threshold could actually be as low as 10 per cent, if it spreads more rampantly among the most socially active. This is because they are into contact with others more regularly and are, therefore, more likely to spread the illness.

Herd immunity without a vaccine is considered a controversial route for getting out of the pandemic because it gives a message of encouraging the spread of the virus, rather than containing it.

No 10 was even forced to deny herd immunity was the strategy after Boris Johnson’s chief aide Dominic Cummings reportedly confirmed the plan at a private event back in February, allegedly saying it was ‘too bad’ if it meant ‘some pensioners die’.

And leaked emails published last month showed that both Sir Patrick Vallance and Professor Chris Whitty faced backlash from academics over the controversial ‘herd immunity’ approach that was further discussed in March.

Meanwhile, unlike most European nations, Sweden never imposed a lockdown and kept schools for under-16s, cafes, bars, restaurants and most businesses open when the disease hit Europe in February.

Researchers have even suggested that the Scandinavian nation has since built up a degree of immunity to the virus, with one academic claiming that the virus may now have run out of steam in Sweden.

But data compiled by Our World In Data — a website that has tracked the pandemic since it began — suggests cases have began to rise again over the past few weeks. For instance, Sweden’s seven-day average of daily infections stood at 560 on October 1, up from 250 at the start of September.


Deciding who should be protected from the virus and then isolating only them would be too complex and wouldn’t work, experts say. 

Boris Johnson said this week that ‘we can’t let the virus rip’, shooting down the idea that herd immunity could emerge as a plausible strategy.

The concept of herd immunity relies on a large proportion of people becoming immune to a virus – through vaccination or past infection – meaning it spreads much more slowly or not at all through the population. 

Scientists have suggested that between 40 and 70 per cent of people may need immunity for this to work with Covid-19. There is currently no proof that anyone gets long-term protection after having the disease once. 

In their letter the scientists, led by Dr Deepti Gurdasani from Queen Mary University in London, said: ‘Any pandemic management strategy relying upon immunity from natural infections for Covid-19 is flawed…

‘There is no evidence for lasting protective immunity to SARS-CoV-2 following natural infection, and the endemic transmission that would be the consequence of waning immunity would present a risk to vulnerable populations for the indefinite future. 

‘Such a strategy would not end the Covid-19 pandemic but result in recurrent epidemics, as was the case with numerous infectious diseases before the advent of vaccination. 

‘It would also place an unacceptable burden on the economy and healthcare workers, many of whom have died from Covid-19 or experienced trauma as a result of having to practise disaster medicine. 

‘Additionally, we still do not understand who might suffer from long Covid. Defining who is vulnerable is complex, but even if we consider those at risk of severe illness, the proportion of vulnerable people constitute as much as 30 per cent of the population in some regions.

‘Prolonged isolation of large swathes of the population is practically impossible and highly unethical.’

The paper advocates instead for governments – signatories came from the UK, US, Sweden, Switzerland, Germany, France, Australia, Spain, Israel, Italy and Malaysia – to focus on stopping the coronavirus.

It concluded: ‘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. 

‘We cannot afford distractions that undermine an effective response; it is essential that we act urgently based on the evidence.’

The paper echoes the comments of Prime Minister Boris Johnson in the House of Commons this week.

In a rebuttal to the Great Barrington declaration and the growing momentum behind calls to let the virus spread among young people, who currently make up the majority of cases in Britain, the PM said: ‘I understand the frustration of those who have been chafing under the restrictions, the sacrifices they have made.

‘But if we were to follow that course and let the virus rip, then the bleak mathematics dictate that we would suffer not only an intolerable death toll from Covid, we would put such huge strain on our NHS, with an uncontrolled second spike that our doctors and nurses would be simply unable to devote themselves to the other treatments for cancer, for heart disease and hundreds more that have already been delayed and that would be delayed again, with serious long term damage to the health of the nation.

‘And I am afraid it is no answer to say that we could let the virus take hold among the young and fit while shielding the elderly and vulnerable.

‘Because the virus would then spread with such velocity in the general population that there would be no way of stopping it from spreading among the elderly.

‘And even if the virus is less lethal for the under 60s, there will still be many younger people for whom, alas, it remains lethal.’

The entire letter can be read online at The Lancet


Kristina Alexanderson (Stockholm) 

Christian L. Althaus (U. of Bern)

Nisreen Alwan (U. of Southampton)

Rochelle Burgess (UCL)

Simon Ashworth (Imperial Coll. NHS)

Rupert Beale (Francis Crick Institute)

Laura Bear (LSE)

Nahid Bhadelia (Boston University) 

Debby Bogaert (U. of Edinburgh)

Reinhard Busse (Berlin)

Colin J. Carlson (Georgetown U.)

Yves Charpak (France)

Tim Colbourn (UCL)

Anthony Costello (IndieSAGE)

Jennifer Dowd (U. of Oxford)

John Drury (University of Sussex)

Isabella Eckerle (Geneva) 

Jacques Fellay (Lausanne)

David Fisman (University of Toronto)

Karl Friston (UCL)

Valentina Gall (U. of Groningen)

Lynn Goldman (G. Washington U.) 

Trisha Greenhalgh (Oxford)

Deepti Gurdasani (Queen Mary U.)

Adam Hamdy (Ligandal)

William Hanage (Harvard)

Emma Hodcroft (University of Basel) 

David Hunter (University of Oxford)

Zoë Hyde (U. of Western Australia) 

David Ingleby (U. of Amsterdam) 

Paul Kellam (Imperial College London)

Michelle Kelly-Irving (Inserm, France) 

Kamlesh Khunti (U. of Leicester)

Ilona Kickbusch (Switzerland)

David King (Mount Sinai)

Krutika Kuppalli (U. of South Carolina)

Alastair Leyland (U. of Glasgow)

Marc Lipsitch (Harvard) 

Maimuna Majumder (Boston)

Jose Martin-Moreno (U. of Valencia) 

Martin McKee (IndieSAGE)

Paul McLaren (U. of Manitoba)

Alan McNally (U. of Birmingham) 

Michael Mina (Harvard)

Julian Mamo (EPHA)

Susan Michie (UCL) 

Melinda Mills (U. of Oxford)

Moran-Gilad (Ben Gurion University)

Stuart Neil (King’s College London)

Ali Nouri (Fed. of American Scientists)

Anna Odone (Università Vita-Salute)

Christina Pagel (UCL)

Alexandra Phelan (Georgetown U.)

Deenan Pillay (UCL)

Dominic Pimenta (HEROES)

Saskia Popescu (George Mason U.)

Viola Priesemann (Max Planck Inst.) 

Seth J. Prins (Columbia University)

Angela L. Rasmussen (Columbia) 

Stephen Reicher (U. of St. Andrews)

Walter Ricciardi (Italy)

Ken Rice (University of Edinburgh)

Johanna Riha (Kuala Lumpur)

Harry Rutter (University of Bath)

Gabriel Scally (IndieSAGE)

Carlo Signorelli (U. Vita-Salute)

Joshua Silver (Oxford)

Tara Smith (Kent State University) 

Devi Sridhar (U. of Edinburgh)

Anthony Staines (Dublin City  U.) 

Charles Swanton (Francis Crick)

Rochelle P. Walensky (Harvard) 

Kevin Watkins (Save the Children)

Clare Wenham (LSE) 

Robert West (UCL)

Gavin Yamey (Duke University)

Kit Yates (University of Bath)

Hisham Ziauddeen (U. of Cambridge) 


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