Definitions of priority groups vary across countries. To arrive at a globally consistent concept, the tracker includes all people aged 60+ as well as medical workers (specifically physicians, nurses and midwives on the basis of the WHO’s Health Workforce Accounts) who are under 60 (to avoid double counting). Various refinements are possible to include those with pre-existing conditions.
We use the World Development Indicator data set of the World Bank on Health, Nutrition and Population Statistics to retrieve global information on physicians, nurses and midwives and filter out the latest observation. The WHO’s Health Workforce Accounts are then used to calculate the share that is younger than 60 (to avoid overlap with the 60+ population, which is separately included).
A number of adjustments are made to deal with data gaps. In cases where information is missing on the 55-64 or 65+ buckets, we apply the share of that age cohort observed in peer groups. For this purpose, we calculate the median share by income classification and apply that to the missing values. Finally, since the Health Workforce Accounts do not provide more granular data of the 55-64 age cohort, we divide this cohort into 2 to get an estimate of the 60- group within this cohort.
More refined estimates of the health workforce will undoubtedly be available at the country level. In the interest of building a global dataset we rely however on this method which has the advantage of imposing transparent assumptions on all countries in an equal way.
The distribution of vaccine doses across countries is described on the basis of data on the actual doses administered. The reasons why the numbers may be low can vary widely and include international vs domestic factors as well as supply versus demand factors. At this moment in time, however, the most likely reason for low numbers is related to international supply bottlenecks.
The data does not measure actual vaccination of the priority group, which is currently impossible to consistently assess at the global level given data gaps. Instead, it describes on the basis of the size of the priority group and the number of doses administered the extent to which the priority group could have been covered through the vaccination efforts up through the latest available data point.
This assumption relies on governments acting as “benevolent social planners” interested to vaccinate their most vulnerable groups first. It also requires common agreement about who the most vulnerable groups are. In the context of this chart, it furthermore requires that the vulnerable group concept adopted coincides with the definition of the priority group of medical professionals under 60 and the entire 60+ population. In sum, there are plenty of reasons why actual coverage of priority populations may differ.
An additional complication pertains to the treatment of doses. The vaccine landscape is diverse with different treatment protocols in terms of the number doses that need to be administered, the dosage of each dose and the length of time between them. Vaccines differ in terms of their efficacy and deviations from the prescribed protocol dilute efficacy in uncertain ways. This matters as countries consider to speed up vaccination by e.g. changing, reducing or delaying doses.
The approach taken here in the face of this diversity of possibilities is to express vaccination coverage in terms of single doses at full dosage as per the treatment protocol and convert all vaccines to a common denominator of the double-dose protocol. This means that for the purpose of considering whether someone has achieved full vaccination we require that two doses have been administered.
Double-dose equivalence is imposed on single-dose vaccines by simply multiplying the number of single-doses administered by two. In this way, when adding up single doses of single-dose protocols and single doses of double-dose protocols, we can keep the threshold of 200% vaccine coverage as indicating full coverage.
Since the analysis here focuses on the ability to fully vaccinate the priority group (which, again, requires 200% coverage), the real-world distinction between people fully or partly vaccinated makes no difference. The thought experiment here indeed abstracts from real-world possibilities where, for example, preference is given to partly vaccinating the full population as opposed to fully vaccinating the priority segment. In this thought experiment, the priority group gets full priority and no one receives a single shot until this group is fully vaccinated under the existing protocols of whatever vaccine is being administered.
Note that for visualization purposes we censor the priority group coverage ratio at 200%. Given the double-dose equivalence transformation, this is when the country achieves universal coverage of the priority group population. Note that full coverage at 200% is evaluated at the level of the country, not the income group aggregate. In other words, if a country has administered many more vaccines that is required to cover its priority group, that surplus is not recirculated towards other countries in the group.