Herd immunity is when large portions of the public are exposed to a disease and become immune, but it is usually talked about in the context of vaccination programmes.
The term has been bandied about in the last few weeks as the UK devised policies for tackling coronavirus.
Health Secretary Matt Hancock denied that the government was taking a herd immunity approach to the pandemic which could risk a lot more deaths than social isolation measures. The British Government ended up taking lockdown approach and Boris Johnson urged the nation to stay at home.
In contrast to measures implemented in countries across the world, Sweden has taken a liberal approach to combating the infectious virus.
Here, we take a closer look at what the term means and how Sweden's response differs from other countries'.
What is herd immunity?
This is where much of the population is protected from a contagious disease because a significant proportion have become immune through either surviving infection or through becoming immune.
England’s chief scientific adviser Sir Patrick Vallance previously said that a herd immunity approach could be beneficial.
But Mr Hancock denied that was the Government’s policy, describing it as a “scientific concept”.
The approach had been criticised by a group of scientists from UK universities, who said it risks “many more lives than necessary”, and was called into question by the World Health Organisation (WHO).
The UK Government acted slower than many other nations in ordering businesses to close and banning large gatherings to stymie the spread of Covid-19.
In part, Prime Minister Boris Johnson fears introducing “Draconian” measures too quickly could see the public ignore them.
What is herd immunity?
In the end it followed in the footsteps of most countries in the world and adopted isolation measures.
Before entering lockdown, Mr Hancock told Sky’s Sophy Ridge: “What we will do is listen to all the credible scientists and we will look at all the evidence.
“Herd immunity is not our goal or policy, it’s a scientific concept. Our policy is to protect lives and to beat this virus.”
WHO spokeswoman Margaret Harris has also said “action” is needed over “theories” while there is insufficient knowledge of the science of the coronavirus.
What has Sweden been doing?
The streets of Stockholm are quiet but not deserted amid the coronavirus outbreak.
People still sit at outdoor cafes in the centre of Sweden’s capital. Vendors still sell flowers, teenagers still chat in groups in parks and some still greet each other with hugs and handshakes.
Swedish authorities have advised the public to practise social distancing and to work from home, if possible, and urged those over age 70 to self-isolate as a precaution.
Yet compared to the lockdowns imposed elsewhere in the world, the government’s response to the virus allows a liberal amount of personal freedom.
Standing at bars has been banned in Sweden, but restaurant customers can still be served at tables instead of having to take food to go.
High schools and universities are closed, but pre-schools and primary schools are still running classes in person.
“Sweden is an outlier on the European scene, at least,” said Johan Giesecke, the country’s former chief epidemiologist and now adviser to the Swedish Health Agency, a government body. "And I think that’s good.”
Other European nations “have taken political, unconsidered actions” instead of ones dictated by science, Mr Giesecke asserted.
It remains unclear how long Sweden’s exceptional state will last.
However Prime Minister Stefan Lofven, warned the country would face “many tough weeks and months ahead”. He announced that as of Sunday, gatherings would be limited to 50 people instead of 500.
He noted that weddings, funerals and Easter celebrations would be affected.
For now, the Swedish government maintains that citizens can be trusted to exercise responsibility for the greater good and will stay home if they experience any Covid-19 symptoms.
Many Swedes are indeed keeping the recommended distance from others.
But some scientists have criticised the approach as irresponsible during a worldwide pandemic that has already killed over 21,000 people in Europe.
In an open letter to the government, some 2,000 academics called for greater transparency and more justification for its infection prevention strategy.
Sten Linnarsson, a professor at Karolinska Institute, a prominent medical university in Sweden, said the concern centres on “the assessments and the course that the Swedish government has taken through this epidemic, and especially because there is really a lack of scientific evidence being put forward for these policies”.
Mr Linnarsson compared Sweden’s handling of the virus to letting a kitchen fire burn with the intent of extinguishing it later.
“That doesn’t make any sense. And the danger, of course, is that it burns the whole house down,” he said.
Sweden’s current chief epidemiologist, Anders Tegnell, argued that even if the country’s comparatively permissive policies are an anomaly, they are more sustainable and effective in protecting the public’s health than “drastic” moves like closing schools for four or five months.
Sweden, a nation of 10 million, had a total of 3,447 confirmed virus cases and 105 deaths by Sunday, according to a Johns Hopkins University tally. However, there has been limited testing, with some 24,500 tests conducted by Wednesday, according to official statistics.
“The goal is to slow down the amount of new people getting infected so that health care gets a reasonable chance to take care of them. And that’s what we all do in every country in Europe,” Mr Tegnell said. “We just choose different methods to do it.”
Susanna Moberg, a 63-year-old retired teacher, said she trusted the government and also believes Sweden’s experience with the virus will not be as dire as Italy’s, which has by far the most virus-related deaths in the world at more than 10,000.
“I’m not so worried. I’m not 70 years yet. And my children are not sick so we will go to a restaurant on Sunday,” Ms Moberg said.
“We said ‘Everybody is well and the restaurant is open’. So we will go there to celebrate. We can’t stay at home the whole day, all week.”
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