This chart shows the evolution over time of the ‘relative severity ratio’ at the global level.
The relative severity ratio relates COVID-19 mortality to the level and profile of pre-pandemic mortality. The ratio itself is defined simply as the ratio between (1) the total weekly number of deaths with COVID-19 as the underlying cause and (2) the total number of all-cause deaths in 2019 during a similar length of time. In light of data constraints and to foster global comprehensiveness, we take total all-cause mortality for 2019 and scale it down to the period of a week for the comparison under (2).
The relative severity ratio is then used to make two types of comparisons.
Note that the expression of mortality in relative terms is a useful way to communicate the severity of the pandemic. Countries will have adapted to their specific patterns of mortality. Deviations from this pattern may create pressure points, such as on the health system. Comparisons with previous patterns give a country-specific and intuitive flavor of the severity of the COVID-19 pandemic. A statement such as “COVID-19 is claiming more lives than the top cause of death did in 2019” may convey a better feel for the severity of the pandemic than a reference to a mortality rate (total deaths per 100k people).
In the above chart, we show the evolution of weekly relative severity and how it compares with the proportionate mortality rates of the top causes of death in 2019 (specifically the top 2nd and top 3rd cause).
Note that comparisons with top causes of death are with reference to the 133 disease families of the 2019 Global Burden of Disease study (at the third level of ICD-10). We generally select the top nth cause of death, which most closely approximates the peak COVID-19 severity ratio from below. More details on the concept of relative severity are in the paper of Schellekens and Sourrouille (2020) that developed the concept, which can be found here.