Large antibody study in Spain
https://www.thelancet.com/pdfs/journ...20)31483-5.pdf
5% positive across the country, up to 14% in some areas (Madrid)
"The majority of the Spanish population is seronegative to SARS-CoV-2 infection, even in hotspot areas.
Most PCR-confirmed cases have detectable antibodies, but a substantial proportion of people with symptoms compatible
with COVID-19 did not have a PCR test and at least a third of infections determined by serology were asymptomatic.
These results emphasise the need for maintaining public health measures to avoid a new epidemic wave."
47 million population
5% of 47 million = 2.35 million implied infections
300k cases
29k confirmed deaths
45k excess deaths in 2020
45k excess deaths / 2.35 million implied infections = 1.9% infection fatality rate