The architect of Sweden's no-lockdown strategy said up to 30% of its population could now be immune to COVID-19, a claim not supported by data

• The head of Sweden's lockdown-free coronavirus response claimed that as many as 30% of the country's population could be immune to COVID-19 in an interview with The Observer.
  
• Anders Tegnell suggested the figure despite all available studies reporting much lower of antibodies in the Swedish population — for example, around 10% of Stockholm, which is the worst-affected region.
• It is also not yet clear to what extent having antibodies protects a person from catching COVID-19.

The architect of Sweden's lockdown-free coronavirus strategy claimed that almost a third of the country's population could now immune to COVID-19 — a theory not backed up by any hard evidence.

Anders Tegnell, the chief epidemiologist at Sweden's Public Health Agency, told The Observer that immunity levels could have risen to above 30% in some parts of the country.

He said that the recent drop in Sweden's cases could mean there is an immunity level in Sweden's population of "20%, 30%, maybe even slightly more in some areas."

Tegnell is widely credited as the architect of Sweden's unusual response to the coronavirus pandemic, in which the country decided not to institute a widespread lockdown, and put in place relatively few restrictions.

His claim about immunity came while trying to explain the drop in Sweden's cases over the past month.

Tegnell said that seasonal factors, like schools and offices closing for Sweden's summer holidays, were not enough to explain the drop in cases on their own.

"Exactly why this happened at that time and why it was so quick and sudden, is difficult for us to understand," he said.

"But we believe that the increasing number of immune people in the population must have something to do with it."

Despite Tegnell's theory, researchers have so far reached few solid conclusions on immunity to COVID-19, and how it may work.

People who caught the virus usually have antibodies, which can be measured by tests. But is is not clear whether having antibodies offers total — or even partial — immunity to COVID-19, and how long the effect may last.

Studies measuring antibodies in Sweden have not shown levels nearly as high as the 20% or 30% cited by Tegnell.

In June, data from its Public Health Agency showed antibodies in around 10% of people in Stockholm, which was the worst-affected region.

Tegnell said the reason that studies have not supported his thesis is because it is hard to get a good sample.

He told the Observer: "It's very difficult to draw a good sample from the population, because obviously, the level of immunity differs enormously between different age-groups between different parts of Stockholm and so on, and that's why when we measure one group we get 4% to 5%, and when we measure another group they're up to 25%."

Tegnell had said in April that he expected 40% of people in Stockholm, Sweden's capital, to be immune by the end of May.

A study in late May suggested that 6.1% of the population of Sweden had developed coronavirus antibodies.

Some virologists in Sweden reject the theory that cases are falling because of immunity.

More than 5,700 people have now died of the coronavirus in Sweden — a figure that's far higher than in neighbouring countries, which have similar political systems and social customs.

Per capita, its deaths are more than five times higher than Denmark's, more than 11 times higher than Norway's, and almost 10 times higher than Finland's.

Prof. Jan Albert, an infectious diseases expert at Sweden's Karolinska Instituet, warned Business Insider last week that Sweden could see further spikes in virus cases, or even a second wave of cases, particularly as summer holidays end.

We definitely have come down from a peak, but whether we will see an increase again later in the year, especially when workplaces and schools open up again, we don't know."

"It's likely that we will see at least smaller outbreaks and possibly some kind of second wave or peak."