The number of COVID-19 fatalities across different countries varies widely, leading to ambiguity about the mortality rate of the disease. This variation may be due to the ages of individuals tested and identified.

The objective of this research is to measure the contribution of distortions from the age distributions of confirmed cases to the disease-related mortality across populations.

The research team conducted a cross-sectional demography study using aggregate data on COVID-19 cases and deaths by age. The research setting included population-based data from countries like China, the US, France, Germany, South Korea, the Netherlands, Italy, Switzerland, and Spain. Age-specific COVID-19 case fatality rates (CFRs) and age-specific population shared by each country were measured during this research.

The observed CFR varies widely, with the highest rates in Italy (9.3%) and the Netherlands (7.4%), with the lowest rates being in South Korea (1.6%) and Germany (0.7%). The adjustment for the age distribution of cases explains 66% of the variation across countries, with an age-standardizing median CFR of 1.9%. A more extensive study of 95 countries indicated that the variation in COVID-19 CFRs is 13 times more than what would be expected as per just the differences in the age-composition of countries.

The research concluded that selective testing and identifying older cases significantly wraps estimates of the lethality of COVID-19 within people. However, accurate comparisons by removing age distortions would be essential for precisely monitoring the pandemic overtime.