Sweden's state epidemiologist has said the country has been "surprisingly slow" at achieving immunity.
The death toll in Sweden has just passed 5000 and the Scandinavian nation has one of the highest mortality rates in the world with a per capita death rate of 487 per 1 million people - about 10 times higher than neighbouring Norway.
Yet an analysis by Werlabs AB of 50,000 tests showed that only 14 per cent of those living in the Stockholm region tested positive for coronavirus antibodies.
In Bergamo, considered to be the centre of Italy's deadly outbreak, about 57 per cent of people had antibodies.
Sir Patrick Vallance, the UK's chief scientific adviser estimated that 60 per cent of people would need to be infected to achieve herd immunity from the novel coronavirus.