Demography acts as a beacon towards which pandemic mortality outcomes gravitate. Accordingly, demography (the combination of population size and age structure) represents a structural trend that has supported (and will continue to support) a shift of the mortality burden of the pandemic towards the developing world.
The reason is straightforward. Developing countries are on average younger relative to their own demographic pyramids, but because they are so much more populous than the “older” high-income countries their elderly populations outsize those in richer countries by a significant margin.
The simulations in the chart (red bar on the right) isolate the effect of demography on mortality outcomes across income groups as summarized in their share in the global death toll. The simulation reflects a counterfactual where all other variables are held constant. That means everyone gets infected at the same rate and faces the same age-adjusted infection fatality risk (capturing the age-discriminating nature of COVID-19).
The counterfactual simulations are a thought experiment to interpret the role of demography. They should not be interpreted as forecasts as there are many other confounding factors that affect mortality. At the same time, we do see that the mortality share has evolved rather dramatically since the start of the pandemic into the direction of what these demographic beacons suggest (the dark and light blue bars on the left and in the middle).
The simulations suggest that given their older age structure we should expect that high-income countries attract a higher share of mortality than their share in global population. At the same time, global demography would indicate that the share of high-income countries would be lower than what it is now if other factors than demography are kept constant. From this angle, the observed inequality in the mortality burden between rich and poor countries is excessive relative to what demography would indicate.
More details on the methodology underpinning this chart can be found in our paper.