Applied to Finnish data, the demographic scaling model estimates that more than 14 000 people have already been infected with COVID-19 - which is about one-and-a-half times the number of confirmed cases, 9 682, as of September 27, 2020. In the early stages of the pandemic, the underestimation of the confirmed numbers was even higher. For example, on May 16, 2020, the number of confirmed cases was 6 286, whereas the estimated true number is almost twice as large, 12 150.
“Put into relative terms, 0.3% of the 5.5 million Finns are estimated to have been affected by COVID-19 yet,” says university lecturer Christina Bohk-Ewald from the Center for Social Data Science at the University of Helsinki.
Even though the estimated number of infections is markedly higher than the number of confirmed cases, the course of the coronavirus pandemic has been comparatively mild in Finland so far. This is shown when comparing the number of estimated infections in Finland with those in the U.K., Italy, France, and Spain, as of September 27, 2020. In this sample of five European countries, the U.K. is the country with the most people who have been infected with COVID-19, 1.6 million, while Spain is the country with the largest COVID-19 infection prevalence, 3%.
“Across these five countries, the estimated numbers of COVID-19 infections are, on average, three times larger than the numbers of confirmed cases,“ says Bohk-Ewald.
How critically important the true numbers of COVID-19 infections are for decision makers, shows the practical example of implementing control measures in due time in order to effectively prevent the pandemic to spread further.
“If travel restrictions were based on the true numbers of COVID-19 infections, they would probably be imposed much earlier than if they were based on confirmed cases. Good estimates of the numbers of COVID-19 infections could perhaps help to save valuable time,“ Bohk-Ewald states.
Many people suspect that the coronavirus pandemic is far more widespread than commonly known, and that the confirmed cases are just a lower estimate of the true numbers of people who have been actually infected with COVID-19. But it is still unknown how many more people have been affected by COVID-19 than the numbers of confirmed cases suggest.
Publication: This article has been accepted for publication in the International Journal of Epidemiology, published by Oxford University Press. (A preprint is available on medRxiv: doi.org/10.1101/2020.04.23.20077719)
The R source code of the demographic scaling model is freely available here:
Christina Bohk-Ewald, University Lecturer for Applied Data Science and Demography, Center for Social Data Science, University of Helsinki, firstname.lastname@example.org
Christian Dudel, Research Scientist, Max Planck Institute for Demographic Research, email@example.com
Mikko Myrskylä, Professor for Social Data Science, Center for Social Data Science, University of Helsinki & Director, Max Planck Institute for Demographic Research, Germany. Email firstname.lastname@example.org