Note: Charts current as of date above; text updated on January 14, 2021.
Since mid-December the world has experienced a major escalation of the pandemic, which reflects the combined spread of Omicron and Delta at a time where the Northern Hemisphere experiences cooler weather and the risk of indoor exposure rises. The general pattern thus far has been for the trajectory of cases to be explosive while the impact on mortality remains muted compared to earlier waves. But how well do these patterns hold up when we examine them more closely?
In what follows, we document the scale of escalation of the current Omicron/Delta episode through three different lenses. First, we examine the levels of peak case and mortality rates before and after November 1 at the country level. Second, we examine the relative escalation in case and mortality rates by World Bank income classification. Third, we do the same by World Bank region.
The relative perspective usefully complements the absolute one as it helps control for inequalities in data quality and other structural features as well as previous pandemic performance.
Past performance. The relative scale of escalation also provides useful insights into how severe the recent outbreak is controlling for past performance (e.g. containment efforts, access to quality health care). Country X may have for example have successfully adopted a zero-COVID approach, whereas country Y adopts a more accommodative approach. The relative measurement would control for these differences in stances.
Le’s start off with the absolute comparisons. The chart below plots the peak case rate before and after November 1. The date is chosen to stay well clear of the December period where the major escalation really started. Note that case rates are measured as the 7-day trailing average of daily confirmed cases per 100,000 people. We calculate the peak value of this indicator for both periods. The size of the balloons reflects population size and they are colored according to the World Bank income group the country belongs to.
The chart shows a number of things. First, the peaks during earlier waves have generally been higher for high-income and upper-middle-income countries (HICs and UMICs). Second, the peaks during the current episode have been especially high for almost all HICs, as is demonstrated by their values being well above the 45-degree line. So, in absolute terms, we see the highest degree of escalation among countries that had high case rates to begin with!
We can show the same for the mortality rate (see above). Measured mortality rates in HICs and UMICs tends to be larger than for lower-middle-income and low-income countries (LMICs and LICs) – even though that is not true for excess death rates. But the impact of the most recent wave on mortality rates has been quite different compared to cases. Where mortality rates have been high, they have generally remained high even though there’s been a tendency for the recent peaks to be lower. Unlike the picture for cases, there is no escalation in the mortality rate.
Relative comparisons by income group and region
Let’s now take the relative view and look at how population-weighted averages behave. We first start with the country groupings of the World Bank income classification. Note that the peaks are calculated on these weighted averages. We show the relative increase in peak case and mortality rates before and after Nov 1.
The chart clearly shows that on the cases side the escalation has been major in HICs and LICs, even though the latter will be from a lower base as noted earlier. We also see and escalation among UMICs for cases, but for LMICs so far the peak has remained well below the previous peak (as indicated by a ratio below 1).
On the mortality side, we see that throughout the mortality peak has remained at a fraction of the earlier value. That fraction is not negligible, but compared to the scale of escalation in cases it does appear to be more muted. Note here also that the mortality impact reflects the combined effect of Omicron and Delta.
Interestingly, the degree of relative escalation is rather similar across country groups, which is a curious result to interpret as it will be the combined effect of differences in vaccination profiles, immunity from prior infection, seasonality and other environmental and host-specific factors.
In the chart above, we replicate the same analysis at the level of World Bank regions (see footnote for acronyms). The most serious escalations have happened thus far in ECA and NAM even though they have also been considerable for LAC, EAP and even SSA. That’s for cases. The mortality escalation has thus far remained under 1, meaning lower impact than previous peaks (thus far). But we can already see that the relative mortality impact is very considerable for some regions.
Relative comparisons by country and income
Let’s further unpack this by looking at country detail focusing first on countries grouped by World Bank income group. The chart below shows the relative increases in the case rate. Notice how much Australia stands out currently. The current peak case rate is a lot higher than the previous one and the ratio between the two is dramatically different from what we see in other countries. That reflects of course Australia’s performance in keeping earlier peaks down. It also reflects the difficulties in controlling Omicron.
Below is a visualization without Australia. The other features of the chart become more visible now. The dotted line is at 1, the value of the ratio at which the most recent peak equals the past peak. The tiny horizontal lines show the group averages (which were shown also separately earlier and where we should note that the population-weighted group average may look different than the average of the balloon areas since the identification of the peaks happens at the level of the aggregation).
We can see very severe escalations in a number of countries. It is notable that the dispersion among HICs is greater than for any other income group.
Looking into the mortality impact (see chart below), we see a far more homogenous picture than for cases. We already know that in terms of weighted averages the mortality impact stands at a fraction (below 1) of the peak mortality impact of previous waves. Interestingly, however, there is huge dispersion the averages and we see a major escalation in mortality for a number of countries.
Relative comparisons by country and region
Let us now repeat the same analysis by World Bank region. The chart below shows the values for all countries, including Australia, which again illustrates how much an outlier the country is within the EAP region and beyond.
The chart below takes Australia out of the visualization so we can see the variation among other countries better (note that the regional average for EAP represented by the short horizontal line continues to include Australia). We see huge dispersion around the regional averages especially for the region of ECA, which is Europe and Central Asia. We can also see how EAP is being weighed down by the large bubble, which is China.
Finally, let’s look at the mortality impact by country and region. We already know from the earlier comparison by income that the average relative mortality impact has been muted even though there are important exceptions. Interestingly, as we can see here, these exceptions occur in multiple regions, including several countries in EAP and SSA. These regions have seen a more muted mortality impact as registered in the official data (but also in estimated excess deaths).
In sum, the relative comparisons of the Omicron/Delta escalation capture the scale of the escalation. The general pattern is one of a dramatic escalation of cases, which is currently centered on high-income and low-income countries. The mortality impact has been muted throughout across income groups and regions at a fraction of previous waves, but there are important exceptions.