While most countries went into lockdown as Covid-19 spread rapidly across the world, Sweden took a different approach and allowed the controlled spread of coronavirus among the population in attempts to achieve herd immunity.

"It is clear that not only are the rates of viral infection, hospitalisation and mortality (per million population) much higher than those seen in neighbouring Scandinavian countries, but also that the time-course of the epidemic in Sweden is different, with continued persistence of higher infection and mortality well beyond the few critical weeks period seen in Denmark, Finland and Norway," said, lead author Professor David Goldsmith.

Herd immunity is when enough people are immune to a disease, like Covid-19, that the disease can’t be transmitted as easily and thus provides indirect protection.

It can be achieved either through vaccination or if enough people catch the disease and develop immunity.

For example, clinical and research findings suggest, only severely infected Covid-19 patients acquire antibodies in the immediate and early recovery phase of their illness.

Early research has shown that immunity, even in those who were severely infected, can fade after a few weeks and we’ve seen cases of reinfection.

Research also shows that antibodies are much less commonly found in only mildly ill or asymptomatic patients, which means they are very likely not immune, and so can’t stop the spread of infection amongst the community.

The other problem is number of people who need to catch Covid-19 is higher than what it is currently.

Most experts estimate between 40% to 80% of the population would need to be infected.

One researcher, Gabriela Gomes who studies chaos at the University of Strathclyde, told Hamblin that in order to see declines in Covid transmission we only need 20% of people to be immune.