The Swedish ambassador to the US has expressed her hope that Stockholm will have achieved herd immunity in May, whilst the governor of New York has announced 21.2% of city residents have already developed antibodies against Covid-19.

Ambassador Karin Ulrika Olofsdotter told National Public Radio (NPR) that “about 30 per cent of people in Stockholm have reached a level of immunity”, and she hopes the capital could reach herd immunity “as early as next month.”

The Nordic country has come in for scathing criticism in some quarters following its decision to avoid a lockdown, but officials there argue the best way to deal with the outbreak is to allow younger, healthy people to contract the virus and develop antibodies.

So far, Sweden has a lower rate of deaths per million than a host of European countries in lockdown, but it remains to be seen whether that trend will continue, or how long immunity itself lasts among those who have already carried Covid-19.

The news follows Gov. Andrew Cuomo’s release of the startling results of a state-wide antibody test on 3,000 New Yorker shoppers last week.

Whilst the state average of those who had already been infected and developed antibodies was found to be 13.9%, the rate among residents of New York City was 21.2%.

“What we found so far is that the statewide number is 13.9% tested positive for having the antibodies,” Cuomo said.

“They were infected three weeks ago, four weeks ago, five weeks ago, six weeks ago, but they had the virus, they developed the antibodies and they are now recovered.”

African Americans, Latinos and men tested positive at a higher rate than whites and women, with estimates suggesting 2.7 million people in the entire state of 19.4 million residents have already been infected by the virus.

If accurate, the study indicates that the true mortality rate among carriers of Covid-19 in New York is close to 0.5%, a far lower figure than previously estimated.

Cuomo said the lower rates of infections and antibodies in upstate New York may mean a slower, phased re-opening is more likely in areas that have not yet experienced high levels of spread.

Over 15,000 people have died in New York since the outbreak occurred.