The toll of confirmed coronavirus diagnoses and COVID-19 deaths continues to rise daily, but researchers know that lots of mild or asymptomatic infections are going undetected. Without knowing how many actual infections are out there, public health officials don't have a good way to calculate just how deadly the virus is...
On May 20, the Swedish public health authorities published a preliminary estimate, based on antibody tests in April, that 7.3 percent of Stockholm residents had been infected with the disease, with an overall national rate of around 5 percent. Given the current number of deaths attributed to COVID-19, the yields a roughly calculated national infection fatality rate (IFR) of 0.78 percent and one for Stockholm of 1.1 percent.
A preprint of an Italian study released on May 11 tries to figure out the what percentage of people in the Milan metropolitan region were already infected by the virus from late February to early April. They saw a gradual increase, eventually reaching an estimated 7.1 percent of the Milan region's population. That yields a regional rate of over 2.2 percent.
Spain's reported rate of infection is similar to Sweden's: Researchers at the Carlos III Health Institute estimate that "5 percent of the population has been infected, with variability according to provinces." Spain's national IFR is around 1.2 percent.
A team of French epidemiologists have estimated in Science that 4.4 percent of that country's population has been infected by the virus. The French IFR is about 1 percent.
On May 20, Denmark's State Serum Institute reported the very preliminary results of antibody testing conducted in six cities. They estimate that about 1.1 percent of Danes have been infected.
All of these studies report considerable variability between the regions within each countries, That being said, the main takeaway from these studies is that, as the Norwegian Institute of Public Health put it,
'the much discussed herd immunity appears to be still very far away.'