A recently published update to the ongoing study in Geneva to assess the extent of SARS-CoV-2 infection suggests 10.8% of the population may have been infected in the first wave of infections.
The study, which tests a sample of the population over time for IgG SARS-CoV-2 antibodies, started in early April 2020. The latest figures come from the fifth week of testing, which was concluded on 9 May 2020.
In the first week, 4.8% tested positive for antibodies, a figure that rose to 8.5% and 10.9% in the second and third weeks. In the fourth week the rate fell to 6.6% before rising to 10.8% in the fifth week. The report doesn’t explain why the percentage fell to 6.6% in the fourth week, however it suggests the results should be interpreted with caution.
By 9 May 2020, Geneva had brought the spread of the virus under control – only 82 new infections were recorded between 9 May and 9 June 2020.
If accurate, the recent antibody percentage of 10.8% suggests the infection rate is roughly 11 times higher than the recorded case figure. This would mean 89.2% of Geneva’s population avoided infection during the first wave.
Among participants over 65, 4.1% tested positive for IgG SARS-CoV-2 antibodies, a figure suggesting that 95.9% of this group avoided infection.
If the most recent antibody test results are used to calculate infection rates, the implied population-wide infection fatality rate in Geneva is 0.5%, while the rate for those over 65 is around 8.0%.