Severity in high-income countries

This chart shows the evolution over time of the ‘relative severity ratio’ at the level of the World Bank country group of the high-income countries (HICs) and makes a comparison of COVID-19 mortality with the top causes of death in 2019 at the level of this aggregation. 

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. 

• The severity ratio itself involves a comparison with the level of 2019 mortality. We compare COVID-19 mortality during the pandemic with all-cause mortality in 2019 over the same interval of time. If the ratio is, say, 10% then we COVID-19 deaths mortality is similar in magnitude to about a 10th of the dying that happened in 2019 over a similar interval of time.
• With the severity ratio, we can also make comparisons with the profile of 2019 mortality. Consider the share of deaths due a specific cause (e.g. stroke) in total deaths of 2019. This variable is called the cause-specific proportionate mortality rate. If stroke were the top cause of death in 2019, we could compare its proportionate mortality rate (e.g. 9% in all 2019 deaths) with the COVID-19 severity ratio (10%) and argue that COVID-19 is claiming currently more lives than the top cause of death (stroke) did in 2019 over a similar period. 

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). 

Finally, 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.