Why Covid herd immunity could be ‘twice as high as first thought’
Scientists say some people may be resistant even if they haven’t had the new coronavirus
Two new scientific studies have offered some much-needed hope in the battle against Covid-19, by suggesting that immunity to the disease may be much higher than previously thought.
Although coronavirus antibody testing has found that levels are low even in the cities worst hit by the pandemic, other forms of immune response seem to be more widespread.
Indeed, “public immunity could be as much as twice that found in antibody tests, meaning infection hotspots such as London could be further along the path to herd immunity than thought”, says The Telegraph.
Subscribe to The Week
Escape your echo chamber. Get the facts behind the news, plus analysis from multiple perspectives.
Sign up for The Week's Free Newsletters
From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.
From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.
A natural ceiling?
Scientists have been puzzled by the tendency of the new coronavirus to spread rapidly but then slow down long before they would expect to see herd immunity.
“On the Diamond Princess cruise ship, for example, where the virus is likely to have spread relatively freely through the air-conditioning system linking cabins, only 20% of passengers and crew were infected,” say Sweden-based epidemiology professors Paul W. Franks of Lund University and Joacim Rocklov of Umea University, in an article on The Conversation.
The 20% ceiling on infections has also been seen in outbreaks on military ships and in London, Stockholm and New York, they note.
“This has led to speculation about whether a population can achieve some sort of immunity to the virus with as little as 20% infected” - much lower than the “widely accepted herd immunity threshold” of 60% to 70% suggested by earlier mathematical models.
–––––––––––––––––––––––––––––––For a round-up of the most important stories from around the world - and a concise, refreshing and balanced take on the week’s news agenda - try The Week magazine. Start your trial subscription today –––––––––––––––––––––––––––––––
How T-cells could explain the discrepancy
Recent studies have focused on the role of T-cells, a type of white blood cell that forms part of the human immune system.
T-cells “thwart infections in two different ways”, says Science magazine: by spurring other cells to produce antibodies and by targeting and destroying infected cells. The severity of disease can depend on the strength of these T-cell responses.
And unlike antibodies, which are specific to a particular virus or bacteria, T-cells activated by one infection can protect against an array of similar threats.
As such, people with activated T-cells that are effective against the Covid-19 coronavirus could help to close the gap between the 20% of people with antibodies and the 60% or more needed for herd immunity.
‘A third of us may be immune’
A new study conducted by the Karolinska Institutet in Sweden looked at blood samples from 200 adults, including people with no symptoms of Covid-19.
“In total, 30% of the healthy blood donors were found to have developed ‘T-cell immunity’ – twice the number of cases in which antibodies were detected,” The Telegraph reports.
Whether active T-cells - or indeed antibodies - offer complete protection against the coronavirus is unclear, but scientists say that both responses are likely to help the body fight the virus.
“What this means is that we are probably underestimating the number of people that have some type of immunity,” said study co-author Marcus Buggert, an assistant professor at the institute’s Centre for Infectious Medicine.
‘Four in five have some protection’
Another study involving T-cells by researchers at Germany’s University Hospital Tubingen found even more widespread immunity among a total of 365 volunteers.
When their blood was exposed to the new coronavirus, the 180 participants who had previously had Covid-19 showed the strongest T-cell immune response, as had been expected.
“But surprisingly, there was also an immune reaction in 81% of the people (150) who had never had Covid-19,” the Daily Mail reports. “This, the scientists said, was because they had already been infected with one or more of the common cold coronaviruses known to infect humans.”
About a third of all colds are thought to be caused by coronaviruses that predate the new variant which causes Covid-19.
Uneven distribution
If T-cells are a critical part of the body’s defences against Covid-19, low levels of these “immune hunters” in older people could explain why the elderly are so much more likely to die of the disease.
“Young people and those with mild infections are more likely to have a T-cell response than old people,” say disease experts Franks and Rocklov. “We know that the reservoir of programmable T-cells declines with age.”
And if T-cells are most effective against the new coronavirus when they have already fought off a similar infection, this may have helped some countries such as Japan to contain the pandemic more easily than others.
“Exposure to the related virus that caused the epidemic of severe acute respiratory syndrome (Sars) in 2002-04 might have afforded some protection to East Asians against Covid-19,” says The Observer.
–––––––––––––––––––––––––––––––For a round-up of the most important stories from around the world - and a concise, refreshing and balanced take on the week’s news agenda - try The Week magazine. Start your trial subscription today –––––––––––––––––––––––––––––––
Create an account with the same email registered to your subscription to unlock access.
Sign up for Today's Best Articles in your inbox
A free daily email with the biggest news stories of the day – and the best features from TheWeek.com
Holden Frith is The Week’s digital director. He also makes regular appearances on “The Week Unwrapped”, speaking about subjects as diverse as vaccine development and bionic bomb-sniffing locusts. He joined The Week in 2013, spending five years editing the magazine’s website. Before that, he was deputy digital editor at The Sunday Times. He has also been TheTimes.co.uk’s technology editor and the launch editor of Wired magazine’s UK website. Holden has worked in journalism for nearly two decades, having started his professional career while completing an English literature degree at Cambridge University. He followed that with a master’s degree in journalism from Northwestern University in Chicago. A keen photographer, he also writes travel features whenever he gets the chance.
-
5 conspiratorial cartoons about FEMA
Cartoons Artists take on paper towel politics, king-sized conspiracies, and more
By The Week US Published
-
Take an island-hopping trip around Brittany
The Week Recommends From neolithic monuments to colourful harbours, there is much to discover
By The Week UK Published
-
Why has Joker: Folie à Deux divided critics?
Talking Point The sequel to Joker is 'staggeringly inept' in its attempts to explore mental health issues – but Lady Gaga is 'magnetic'
By The Week UK Published
-
Long Covid: study shows damage to brain's 'control centre'
The Explainer Research could help scientists understand long-term effects of Covid-19 as well as conditions such as MS and dementia
By The Week UK Published
-
FDA OKs new Covid vaccine, available soon
Speed read The CDC recommends the new booster to combat the widely-circulating KP.2 strain
By Peter Weber, The Week US Published
-
Mpox: how dangerous is new health emergency?
Today's Big Question Spread of potentially deadly sub-variant more like early days of HIV than Covid, say scientists
By The Week UK Published
-
What is POTS and why is it more common now?
The explainer The condition affecting young women
By Devika Rao, The Week US Published
-
Brexit, Matt Hancock and black swans: five takeaways from Covid inquiry report
The Explainer UK was 'unprepared' for pandemic and government 'failed' citizens with flawed response, says damning report
By Harriet Marsden, The Week UK Published
-
Should masks be here to stay?
Talking Points New York Governor Kathy Hochul proposed a mask ban. Here's why she wants one — and why it may not make sense.
By Anya Jaremko-Greenwold, The Week US Published
-
Covid might be to blame for an uptick in rare cancers
The explainer The virus may be making us more susceptible to certain cancers
By Devika Rao, The Week US Published
-
Long Covid and chronic pain: is it all in the mind?
The Explainer 'Retraining the brain' could offer a solution for some long Covid sufferers
By The Week UK Published