Just one in 14 Swedes have developed Covid-19 antibodies casting doubt on the country's herd immunity response to the coronavirus.
A Swedish study found that only 7.3 percent of Stockholmers had developed antibodies by late April.
The country's herd immunity strategy was championed by Chief Epidemiologist Anders Tegnell.
He recommended adopting voluntary measures against the virus, rather than a mandatory lockdown like those imposed by many other countries, which has divided opinion at home and abroad.
Sweden has kept most schools, restaurants, bars and businesses open even as much of Europe hunkered down behind closed doors.
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The policy has exposed it to criticism with death rates running far higher than in Nordic neighbours, even if much lower than in countries such as Britain, Italy and France that shut down.
The number of Covid-19 patients in intensive care in Sweden has fallen by a third from the peak in late April and health authorities say the outbreak is slowing.
However, Sweden recorded the highest number of Covid-19 deaths per capita in Europe over a seven day period.
The antibody study aimed to find out whether herd immunity was achievable.
If it is, enough people in the population would have developed immunity to the infectious disease to be able to effectively stop it from spreading.
The findings were roughly in line with models predicting a third of the Swedish capital’s population would have had the virus by now and where at least limited herd immunity could have set in, the Swedish Health Agency said on Wednesday.
“It is a little bit lower (than expected) but not remarkably lower, maybe one or a couple of percent,” Tegnell told a Stockholm news conference. “It squares pretty well with the models we have.”
However, the herd immunity concept is untested for the novel coronavirus and the extent and duration of immunity among recovered patients is equally uncertain as well.
The study drew on some 1,100 tests from across the country although only figures for Stockholm were released.
Unlike the other Nordic countries, Sweden's government has not enforced widespread lockdown measures.
Basing its approach on a so-called 'principle of responsibility', the country has not only kept schools open, but they remain compulsory for children under 16 to attend.
Cafes, bars and restaurants have also stayed open for business, albeit with social distancing measures enforced.
The government has urged people to work from home where possible, while not mandating that anyone does so.
While Sweden's Health Agency officials have stressed herd immunity is not a goal in itself, it has also said the strategy is only to slow the virus enough for health services to cope, not suppress it altogether.
The World Health Organization has warned against pinning hopes on herd immunity.
It said last week global studies had found antibodies in only 1 to 10% of the population, results in line with recent findings in Spain and France.
Bjorn Olsen, Professor of Infectious Medicine at Uppsala University, is among dozen academics who have criticised Sweden’s pandemic response and labelled herd immunity a “dangerous and unrealistic” approach to dealing with COVID-19.
“I think herd immunity is a long way off, if we ever reach it,” he said.
