Clustering of age standardised COVID-19 infection fatality ratios and death trajectories

Kelly, Thu-Lan; Miller, Caroline; Bowden, Jacqueline A; Dono, Joanne; Phillips, Paddy A

BackgroundAn accurate measure of the impact of COVID-19 is the infection fatality ratio, or the proportion of deaths among those infected, which is independent of variable testing rates between nations. The risk of mortality from COVID-19 depends strongly on age and current single estimates of the infection fatality ratio do not account for differences in national age profiles. In addition, it is unclear whether age influences cumulative death trajectories, or if differences between regions are because of the effect and timing of public health interventions. Our objective is to determine whether (1) infection fatality ratios and (2) death trajectories are clustered into more than one group due to differences in national age profiles. MethodsNational age standardised infection fatality ratios were derived from age stratified estimates from China and population estimates from the World Health Organisation. The infection fatality ratios were clustered into groups using Gaussian mixture models. Trajectory analysis clustered cumulative death rates at two time points, 50 and 150 days after the first reported death. FindingsInfection fatality ratios from 201 nations were clustered into three groups: young, middle and older, with corresponding means (SD) of 0.20% (0.03%), 0.38% (0.11%) and 0.93% (0.21%). At 50 and 150 days, there were two and three clusters, respectively, of cumulative death trajectories from 122 nations with at least 25 deaths reported at 100 days. The first cluster had steadily increasing or stable cumulative death rates, while the second and third clusters had moderate and fast increases in rates, respectively. Fifty-eight nations changed cluster group membership between time points. There was an association between the infection fatality ratio clusters and the change in trajectory clusters between 50 and 150 days (p=0.014). ConclusionDifferences in national age profiles created three clusters in the COVID-19 infection fatality ratio, with the impact on younger nations less than the current estimate 0.5-1.0%. National cumulative death rates were clustered into steady, moderate or fast trajectories. Changes in death rate trajectories between 50 and 150 days were associated with the infection fatality ratio clusters, however evidence for the influence of age on death trajectories is mixed.