219 Countries and Territories around the world have reported a total of 129,495,677 confirmed cases of the coronavirus COVID-19 that originated from Wuhan, China, and a death toll of 2,828,643 deaths.
When calculating the mortality rate, we need:
The number of actual cases. We need to know the number of actual cases (not merely the reported ones, which are typically only a small portion of the actual ones) that have already had an outcome (positive or negative: recovery or death), not the current cases that still have to resolve (the case sample shall contain zero active cases and include only “closed” cases).
The number of actual deaths related to the closed cases examined above.
Considering that a large number of cases are asymptomatic (or present with very mild symptoms) and that testing has not been performed on the entire population, only a fraction of the SARS-CoV-2 infected population is detected, confirmed through a laboratory test, and officially reported as a COVID-19 case. The number of actual cases is therefore estimated to be at several multiples above the number of reported cases. The number of deaths also tends to be underestimated, as some patients are not hospitalized and not tested.
If we base our calculation (deaths / cases) on the number of reported cases (rather than on the actual ones), we will greatly overestimate the fatality rate.
New York State conducted an antibody testing study [source], showing that 12.3% of the population in the state had COVID-19 antibodies as of May 1, 2020. The survey developed a baseline infection rate by testing 15,103 people at grocery stores and community centers across the state over the preceding two weeks. The study provides a breakdown by county, race (White 7%, Asian 11.1%, multi/none/other 14.4%, Black 17.4%, Latino/Hispanic 25.4%), and age, among other variables. 19.9% of the population of New York City had COVID-19 antibodies. With a population of 8,398,748 people in NYC [source], this percentage would indicate that 1,671,351 people had been infected with SARS-CoV-2 and had recovered as of May 1 in New York City. The number of confirmed cases reported as of May 1 by New York City was 166,883 [source], more than 10 times less.
