This is a paper by Mikko Paunio M.D., M.H.S., an adjunct professor in general epidemiology at the University of Helsinki, Department of Public Health. In the course of his carer he has worked at the University of Helsinki, Johns Hopkins Bloomberg School of Public Health, the European Commission, the World Bank, and the Ministry of Social Affairs and Health. His current position is Medical Counselor, Ministry of Social Affairs and Health in Finland. You can see a list of his publications here.
Update: Mikko Paunio has written an addendum to his paper, referring to a number of surveys that have been published since he wrote it that seem to support his hypothesis that many more people have been exposed to the virus than the WHO originally estimated, that at least 50% of people infected are asymptomatic and that large cities like New York are close to herd immunity.How-the-World-got-Fooled-by-COVID-ed-2c