National herd immunity to the coronavirus could build up with just four out of 10 people catching the disease, scientists claim.
Researchers say that immunity among the most socially active people in a country could protect those who come into contact with fewer others.
Previous estimates have suggested around two thirds (60 per cent) of a population would have to catch Covid-19 for herd immunity to develop, which would see hundreds of thousands of Britons die if it was achieved without a vaccine.
But this exposure level could be slashed to just 43 per cent, according to scientists from Nottingham and Stockholm.
Herd immunity is a situation in which so many people have become immune to an illness — either by having it or by getting a vaccine — that it can no longer spread.
Government scientists floated the idea at the start of the UK’s outbreak, with the ‘delay’ stage of its original plan based on allowing the virus to spread slowly.
But experts warned that half a million people could die if the country didn’t go into lockdown to stop the virus in its tracks, and officials have since denied that aiming for herd immunity — which could have seen 40million people allowed to be infected — was ever the plan.
Britain is currently nowhere near herd immunity to the coronavirus, with government testing surveys suggesting 5.4 per cent of people have had the illness. This is equal to around 3million people, whereas 43 per cent coverage would require 24million people to be infected.
Scientists suggest that if immunity to the coronavirus develops among more socially active people, this could protect those who interact with fewer people (Pictured: Crowds on Bournemouth beach today)
Scientists at Stockholm University and the University of Nottingham say the key to understanding herd immunity with the coronavirus is looking at social activity.
The virus is considerably more likely to infect people who come into contact with more people — people with busy social lives, schoolchildren, people in large households or those with people-facing jobs, for example.
Meanwhile, many others come into contact with fewer people than average.
The study split people into three groups: Those with an average number of interactions, those with ‘high activity’ — 50 per cent more than average, and those with ‘low activity’ — 50 per cent fewer than average.
If the virus spreads more rampantly among the most socially active group, the level of immunity they build up could protect people in the less active groups.
This is because the more active people come into contact with others more regularly and are therefore more likely to spread the illness.
People with fewer interactions are less likely to catch the disease — because it spreads most often by close contact — and also less likely to pass it on because they’re more likely to go through the illness and recover without seeing anyone.
WHAT IS HERD IMMUNITY?
Herd immunity is a situation in which a population of people is protected from a disease because so many of them are unaffected by it – because they’ve already had it or have been vaccinated – that it cannot spread.
To cause an outbreak a disease-causing bacteria or virus must have a continuous supply of potential victims who are not immune to it.
Immunity is when your body knows exactly how to fight off a certain type of infection because it has encountered it before, either by having the illness in the past or through a vaccine.
When a virus or bacteria enters the body the immune system creates substances called antibodies, which are designed to destroy one specific type of bug.
When these have been created once, some of them remain in the body and the body also remembers how to make them again. This provides long-term protection, or immunity, against an illness.
If nobody is immune to an illness – as was the case at the beginning of the coronavirus outbreak – it can spread like wildfire.
However, if, for example, half of people have developed immunity – from a past infection or a vaccine – there are only half as many people the illness can spread to.
As more and more people become immune the bug 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, according to the Oxford Vaccine Group.
The study hinges on people only being able to catch the virus once, then becoming immune to it in future — but scientists still haven’t worked out whether this is true.
If it turns out not to be, the same result may be achieved by vaccinating the most active section of the population when a vaccine is available, but the UK Government has prioritised jabs for health and care workers, over-50s and seriously ill people.
Professor Frank Ball, Professor Tom Britton and Professor Pieter Trapman — three authors of the new study — said herd immunity from the disease spreading could be ‘substantially lower’ than it would be from a vaccine.
They wrote in the journal Science: ‘Our application to Covid-19 indicates a reduction of herd immunity from 60 per cent… immunization down to 43 per cent in a structured population, but this should be interpreted as an illustration, rather than an exact value or even a best estimate.’
The estimate was based on the reproduction number of the virus (R) being 2.5, meaning that every 10 people would infect another 25 if nobody had any immunity. At the start of the UK’s outbreak it is thought to have been almost 4, according to Imperial College researchers.
A higher R value could mean a greater proportion of people would need exposure for herd immunity to develop, but the new study did not estimate for other figures.
They said that immunity would be stronger in cities, large households and big workplaces.
But this could also reflect where the virus would be most likely to spread in future outbreaks, meaning those in rural areas or smaller offices would have some level of protection simply from being around fewer people.
Blood testing on behalf of the government has found that around 5.4 per cent of people in England have had the virus already. The ballpark is somewhere between 4.3 and 6.5 per cent, according to the Office for National Statistics.
This means around 3million people have had the virus already — nowhere near enough for herd immunity.
But, as per the Stockholm and Nottingham study’s theory, London is considerably closer to herd immunity than other regions.
Testing by Public Health England has found that around 17.5 per cent of people living in the capital have got antibodies to the disease, meaning their immune system has fought it off already.
This varies wildly across the country, PHE data shows, with around 12 per cent of people exposed in the North West and 10 per cent in the East of England, but fewer than 10 per cent in every other region.
Lowest are the South East and North East, where only around four per cent of people appear to have had the illness already.
Herd immunity has been controversial in the UK because the Government appeared to want to aim for it to stop the coronavirus coming back in the future.
But scientists believe that for this to work for Covid-19, around 60 per cent of people would have to have the virus – about 40million people in the UK.
Currently, the coronavirus appears to have a death rate of around one per cent, suggesting that 400,000 people could have died in the process.
Sir Patrick Vallance, chief scientific adviser to the UK Government, spoke about herd immunity in March as if officials were genuinely considering it as an option.
Public Health England blood testing results show the levels of exposure to Covid-19 vary wildly across the UK, from around 17.5 per cent in London to lower than five per cent of people in the South East and North East
When asked about lockdown on March 13 — Italy was already in lockdown by that point – Sir Patrick said that it was ‘impossible’ for a country to attempt to self-isolate its entire population.
He said: ‘We want to suppress it [the virus], not get rid of it completely, which you can’t do anyway, and also allow enough of us who are going to get mild illness to become immune to this to help with the sort of whole population response which would protect everybody.’
Sir Patrick added: ‘We think that this virus is likely to be one that comes back year on year, become like a seasonal virus, and communities will become immune to it, and that’s going to be an important part of controlling this longer term.’
However, public backlash against the plan which would see millions infected and tens or even hundreds of thousands of people die, took herd immunity of the table.
It stopped being mentioned in discussions and 10 Downing Street has denied considering it as a plan ever since.
In a Channel 4 documentary aired earlier this month, Italy’s deputy health minister claimed Boris Johnson had told Italy that he wanted to pursue it.
Pierpaolo Sileri, who is a qualified surgeon and deputy health minister in the Italian government, was diagnosed with the coronavirus himself in mid-March.
He recalled speaking to the country’s prime minister, Giuseppe Conte, who had had a phone call with Boris Johnson on March 13.
Mr Sileri told Dispatches: ‘I spoke with Conte to tell President Conte that I’d tested positive.
‘And he told me that he’d spoken with Boris Johnson and that they’d also talked about the situation in Italy.
‘I remember he said: “He told me that he wants herd immunity”. I remember that after hanging up, I said to myself that I hope Boris Johnson goes for a lockdown.’
The Cabinet Office denied the claims made in the documentary and said: ‘The Government has been very clear that herd immunity has never been our policy or goal.’