Primary and booster vaccination progress compared

Boosters are rolling out more slowly than primary vaccinations and similar patterns of inequality apply

Well into the second year of the global COVID-19 vaccination campaign, countries are rolling out booster programs while continuing to address remaining gaps in primary vaccinations. How does progress under the two programs compare? As it turns out, the booster campaign is proceeding more slowly. Unfortunately, history is repeating itself as demonstrated by the enormous inequality in the performance across nations. 

Persistent inequality

As of today, over 12.7 billion primary doses and 2.5 billion boosters have been administered. We will show a number of static and dynamic visualizations that characterize the inequality across countries in vaccine coverage of the population. We will do so with respect to primary vaccine coverage and later booster coverage.

Let’s first briefly explain the construction of the charts, as they are somewhat complex at first sight. The charts will have the following components:

  • We use a chart with polar coordinates, where countries are displayed on the X axis and grouped by World Bank income group. Countries are labeled by ISO-3 country code in the outer band of the circle. The chart is divided into 4 quadrants, which represent income groups: high, upper-middle, lower-middle and low income countries (HICs, UMICs, LMICs and LICs).
  • The vaccine coverage ratio shown on the Y axis tracks the “intensive margin of vaccination”. This simply refers to the intensity of vaccination and is captured by the vaccine coverage ratio. For primary doses, this is primary doses administered per 100 people, where doses of 1- and 3-dose vaccines are converted into 2-dose equivalents (x2 and x2/3 respectively), That way maximum primary coverage is at  200 regardless the vaccine mix in use.  For boosters, the ratio is booster doses administered per 100 people, We censor the booster ratio at 100 as the data does not allow us to differentiate between booster cycles.
  • The inner band shows the “extensive margin of vaccination”. Whereas the intensive margin captures the intensity of vaccination for those who have started vaccinating, the extensive margin measures the extent to which countries have started to vaccinate at all. The grey component of the inner band shows the share of countries that have not yet started and/or are not reporting yet any data. 
  • Universal coverage is reached when the “donut” turns blue. This would happen at 200 doses per 100 people for the primary series. For boosters, the 100 mark simply reflects aggregate progress towards 100 boosters per 100 people. Aggregate because we conflate booster cycles (one country may have covered all of its people with 1 dose; another may have boosted half of them twice). 
  • Countries are sorted by intensive margin, so we can focus on the overall progress by income group. In the dynamic visualization this will have the effect that countries continually shift (as shown in the outer band with country codes), while the space formed by the blue bars gradually grows. Note that the overall progress by income group is not population-weighted. Countries are given equal weight in the visualization regardless of population size. For population-weighted perspectives by income group, see here and here.

Let’s now proceed to the results. We will first present two static charts that show where we are today in terms of primary and booster coverage. Directly below is the result for primary coverage.

The above chart shows that the gap in primary coverage remains large and regressive. As we can see, there is still a lot of white space in the chart. Since the poorer countries have the largest gaps, primary vaccination progress remains highly regressive. Note how the white space grows as we proceed clockwise from the upper-right quadrant to the upper-left one, from high to low income country groups. The chart also illustrates the diversity of outcomes within income groups, where broadly speaking HICs and LICs show less dispersion than UMICs and LMICs.

Turning now to booster coverage, we see that the gap is much larger. A considerable number of countries have yet to start with booster programs (as indicated by the grey portion of the inner circular bar) and booster coverage levels among those that have started are low, especially in the poorer countries. This is not unexpected as delays in primary vaccination translate into the progress made on boosters.  

Slower progress for boosters

Turning now to booster coverage, we see that the gap is much larger. A considerable number of countries have yet to start with booster programs (as indicated by the grey portion of the inner circular bar) and booster coverage levels among those that have started are low, especially in the poorer countries. This is not unexpected as delays in primary vaccination translate into the progress made on boosters.  

The two dynamic visualizations suggest the following:

  • As to the extensive margin (“whether countries have started vaccinating”), the booster campaign shows much greater delays than the primary campaign in reaching the poorer countries.  For primary vaccinations, it took about 6 months (counting from Dec 2020 till June 2021) before we saw the vast majority of countries in each income group starting their vaccination campaign. For boosters, the delay is even starker, where at 6 months into the time frame (i.e. Feb 2022, about 6 months after Aug 2021) only about 2/3 of UMICs, 1/3 of LMICs and close to 0 LICs had started boosting. Even today, we continue to see the non-participation of several countries.
  • As to the intensive margin (“how well countries are covering their population”), it appears that booster vaccination is proceeding more slowly than primary vaccination. We can see that quite starkly when we compare how fast the blue bars grow in the booster chart with how they grow in the primary vaccine chart over an equivalent period of time. It turns out that overall progress with the boosters is much more drawn-out.

In sum

The most striking result – and this is the key point of this post – is that the dynamic patterns of booster inequality follow very closely the regressive nature that we observed with primary vaccinations. We can clearly see that the vaccination campaign is proceeding more slowly for boosters than primary shots. And the poorer countries are showing the largest gaps. 

The slower progress on the booster front reflects the delays in primary vaccination. After all, one wouldn’t qualify for a booster if the primary cycle hasn’t been completed. But it is clear that other factors are slowing the booster campaign, with fatigue and hesitancy appearing to play an increasing role. 

The outcome is that poorer countries suffer a double whammy: a large gap in primary vaccination that still needs to be filled and an even larger gap in booster vaccination. Together, these gaps compound the vulnerability of the poorer countries in the face of waning immunity and the possibility of new variants. 

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