24/05/2021 17:41 BST

Herd Immunity Against Current Variants Could Be Close, Sage Member Suggests

Sage's Peter Openshaw says 80% would need to have immunity against current Covid strains.

Around 80% of the population would need to have immunity to coronavirus for the country to achieve “herd immunity” against current dominant variants, a leading scientist advising the government has said.

Professor Peter Openshaw, who sits on the Scientific Advisory Group for Emergencies (Sage), said that level of population immunity would protect against the significant spreading of the current dominant Covid variants.

It raises the question of whether of England can reach herd immunity against the Kent and India variants soon.

Official data last month estimated 69.3% of the population in England would have tested positive for Covid antibodies, suggesting they have either been vaccinated or previously infected.

In Wales, the figure is 63.2%, Northern Ireland 63.5% and Scotland 59.2%. 

All the figures are based on the latest Office for National Statistics infection survey, carried out in the week beginning April 19.

With the ongoing success of the vaccination programme, it suggests the UK may be approaching a tipping point towards herd immunity.

But the ONS stressed that detecting antibodies alone is not a precise measure of immunity protection given by vaccines, which all have different efficacies against different variants.

The arrival of new variants could also change the calculation.

Office for National Statistics

Openshaw, a respiratory expert at Imperial College London, was asked by MPs at the Commons public administration committee what level of population immunity would allow the UK to achieve herd immunity against Covid.

He replied: “There is an approximate relationship between the amount of transmissibility of the pathogen and the level of immunity that is required in order to prevent its circulation in the community.

“So with a very, very infectious virus, say measles, you need a very high level of immunity in the population in order to prevent onward spread.

“Whereas with a less infectious virus, even reduced levels of immunity are capable of reducing circulation.

“So we were initially expecting with the Wuhan strain that immunity of something like 60-65% was probably going to be enough to prevent onward transmission.

“With the increment in transmissibility of the 117 [variant] that was originally isolated in Kent or the 617.2, one of the Indian variants, each of those represents an increase in transmissibility which translates into a requirement for greater levels of immunity in the population in order to prevent spread.

“So I would say that in the face of these increased transmissible variants, we are probably looking to achieve something closer to 80% immunity in order to prevent onward transmission.”

Since the last ONS infection survey was carried out in the week beginning April 19, an additional five million more people have received the first dose of the vaccine, according to the government’s Covid data dashboard.

This suggests the figures for people testing positive for antibodies should rise when the latest infection survey figures come out in two days.

Furthermore, an extra 12m or so people have received their second dose since April 19, which will help build up levels of protection and immunity.

UK government Covid data dashboard
The number of Covid vaccinations given in the UK

But appearing at the same committee as Openshaw, virology professor Judith Breuer stressed that as long as Covid keeps mutating with new variants either arising in or entering the country, herd immunity may never be achieved.

She stressed that governments around the world should therefore focus on keeping infection rates low.

“It’s very, very hard to have herd immunity without restricting the import of variants or without it [immunity] being universal,” the University College London director of infection and immunity said.

“As prof Openshaw said, the variants we’re now dealing with are more transmissible than the variants we started with and therefore the herd immunity estimates have to go up.

“And then if we get even higher transmissible variants then the herd immunity estimates will have to go up even further.

“That’s only if you’re only in a closed community as well - if it’s being transmitted all over the world, every time a new variant comes in or a new virus is introduced then you still get outbreaks.

“Herd immunity is a nice concept but it’s going to be a long time before we can actually use it for public health planning.”