The ‘relative severity ratio’ compares COVID-19 mortality to the pre-pandemic mortality profile of individual countries. The first comparison is made through the severity ratio itself, which compares COVID-19 mortality with all-cause mortality in 2019. The second one is the comparison of the severity ratio with cause-specific proportionate mortality rates (the share of deaths due to a specific cause in total deaths).
These comparisons are useful as the expression of mortality in relative terms speaks to the fact that countries may have adapted to their specific patterns of mortality. Deviations from this pattern may create pressure points, such as for example on the health system. Comparisons with previous patterns give a country-specific flavor of the severity of the COVID19 pandemic, which could be used to corroborate realities on the ground.
Comparisons with top causes of death are with references to the 133 disease families of the 2019 Global Burden of Disease study (at the third level of ICD-10) . We select the top nth cause of death which mostly closely approximates the peak COVID-19 severity ratio from below. More details on the concept of relative severity can be found here.
Based on the above methodology, we can construct relative severity ratios for aggregated income groups as well. The aggregation involves two steps (corresponding to the two comparisons mentioned earlier). The first one amounts to aggregating all COVID-19 fatalities as well as all-cause fatalities in 2019 for all countries in the group. This yields the relative severity ratio. The second one requires identifying the top causes of death by proportionate mortality rates for the aggregated groups. This requires aggregation of the 133 disease categories and selection of the most prevalent ones at the level of the group.
The chart above shows that the lowest levels of reported severity are in the group of low-income countries. The levels of severity based on reported mortality statistics are the lower than those of the other income groups (check these out here for HICs, UMICs and LMICs). Mortality due to COVID-19 reached a recent peak there, but that peak only corresponds to the 25th cause of death, which are sexually transmitted infections excluding HIV.
The World Bank has recently launched an interactive tool on its data platform, with which you can calculate the indicator for any country, region or income group. Check out the COVID-19 dashboard on relative severity.