Study shows long road to herd immunity

STOCKHOLM: A Swedish study has found just 7.3% of Stockholmers had developed Covid19 antibodies by late April, which could fuel concern that a decision not to lock down Sweden against the pandemic may bring little herd immunity in the near future.

The strategy was championed by chief epidemiologist Anders Tegnell, whose recommendation for voluntary measures against the virus, rather than a mandatory lockdown, has divided opinion at home and abroad.

Sweden’s strategy of keeping most schools, restaurants, bars and businesses open even as much of Europe hunkered down behind closed doors exposed it to criticism. Its death rates are far higher than in its Nordic neighbours, although much lower than in countries such as Britain, Italy and France that shut down.

The antibody study sought to look into the potential for herd immunity — when enough people in a population have developed immunity to an infection to effectively stop that disease 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 limited herd immunity could have set in, the Swedish Health Agency said yesterday.

‘‘It is a little bit lower [than expected] but not remarkably lower,’’ Tegnell told a Stockholm news conference.

However, the herd immunity concept is untested for the novel coronavirus and the extent and duration of immunity in recovered patients is uncertain.

The study drew on some 1100 tests from across the country although only figures for Stockholm were released.

While Health Agency officials have said herd immunity was not a goal in itself, they have also said the strategy was only to slow the virus enough for health services to cope, not suppress it altogether.

They have said that countries employing wholesale lockdowns could face renewed outbreaks as restrictions were eased.

The World Health Organisation has warned against pinning hopes on herd immunity.

Uppsala University Professor of Infectious Medicine Bjorn Olsen is among a dozen academics who have criticised Sweden’s pandemic response and labelled herd immunity a ‘‘dangerous and unrealistic’’ approach to Covid19.

‘‘I think herd immunity is a long way off, if we ever reach it,’’ he said after the release of the antibody findings.

Sweden’s approach, shaped by a conviction the coronavirus can be slowed but not fully suppressed, is reflected not just in an aversion to quarantines and closures but in a decision to carry out relatively little testing and contact tracing.

Tests are largely restricted to hospital cases and healthcare workers. Weekly test numbers still run at less than a third of the Government’s goal of 100,000, a far lower per capita rate than Sweden’s Nordic peers and below that of most West European countries.

Meanwhile, Sweden’s death toll has risen to 3831, more than three times the combined total of Denmark, Norway, Finland and Iceland, all with similar welfare systems and demographics.