STOCKHOLM • Sweden's hopes of getting help from herd immunity in combating the coronavirus received a fresh blow yesterday, when a new study showed fewer people than anticipated had developed antibodies.

Sweden has opted for a more liberal strategy during the pandemic, keeping most schools, restaurants, bars and businesses open even as much of Europe hunkered down behind closed doors.

While health agency officials have stressed that so-called herd immunity is not a goal in itself, they have also said the strategy is only to slow the virus enough for health services to cope, not suppress it altogether.

However, the study, the most comprehensive in Sweden yet, showed only around 6.1 per cent of Swedes had developed antibodies, well below levels deemed enough to achieve even partial herd immunity.

"The spread is lower than we have thought but not a lot lower," chief epidemiologist Anders Tegnell told a news conference, adding that the virus spread in clusters and was not behaving like prior diseases.

"We have different levels of immunity on different parts of the population at this stage, from 4 to 5 per cent to 20 to 25 per cent," he said.

Herd immunity, where enough people in a population have developed immunity to an infection to be able to effectively stop that disease from spreading, is untested for the novel coronavirus and the extent and duration of immunity among recovered patients is equally uncertain as well.

Sweden surpassed 5,000 deaths from the coronavirus on Wednesday, many times higher per capita than its Nordic neighbours.

Still, cracks have begun to emerge in the political consensus the government has until now enjoyed over its softer approach.

Swedish Prime Minister Stefan Lofven, a Social Democrat, insisted in a weekend televised interview that hospitalisations were down sharply and Sweden's strategy of not imposing a lockdown "was not a failure".

Sweden's political circles broadly supported the decision to not impose a lockdown, as did the general population.

But there has been growing criticism in recent weeks over the government's struggles to get mass testing off the ground, which began in earnest only this week.

The Liberals' parliamentary leader Johan Pehrson said Sweden's softer approach "may have contributed to the high death toll", while Mr Ulf Kristersson, head of the conservative Moderate Party, has called for a commission to be appointed immediately to probe the government's handling of the crisis.

REUTERS, AGENCE FRANCE-PRESSE