Vaccination in reducing the impact of COVID-19 – some considerations

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Immunization is playing a decisive role in reducing deaths from COVID-19


At the end of 2021, almost a year after the start of the application of vaccines against COVID-19, there was a drastic reduction in cases and deaths in a significant number of countries, while in others, a new wave of illness.

To understand this complex situation a little better, we present below some data that list three of the multiple factors that condition and describe the impact of the present pandemic: number of vaccines applied, per 100 inhabitants; age structure and number of deaths per day per million inhabitants.

There is not the slightest pretense here that this has exhausted the understanding of the dimension and heterogeneity of the disease in the world, or of the dynamics of this post-vaccination period, given that there are multiple other factors, including community transmission, the number of cases and the on deaths depends: urban mobility, and sufficient economic support to reduce it; climate, which influences confinement indoors; availability of personal protective equipment (masks, alcohol gel, etc.); number of inhabitants per square meter and in each housing unit; cultural habits, which influence greater or lesser social distance and also the degree of acceptance of vaccination – among others. However, from the following data it is possible to observe some patterns present in the current stage of the pandemic.


Vaccination in the world

The progress of vaccination campaigns in different countries has been very different. In general, the so-called 'developed' countries have had privileged access to vaccine doses, to the detriment of most of those classified as 'developing'. Brazil occupies a particularly dramatic place in this scenario, since, being a country that, in theory, could have started immunization relatively early, it was seriously harmed by the excessive delay in facing the pandemic, the result of a systematic official boycott that has been since from minimizing the effects of the virus to permanent propaganda against social distancing, the use of masks and the adoption of other health precautions. As a consequence, the vaccination process was triggered late, with the subsequent and avoidable loss of hundreds of thousands of lives.

The table below gives the vaccination figures at the present time (November 23, 2021), in terms of the number of doses administered, per 100 inhabitants, in each of the 62 countries listed.

Table 1: Number of doses applied on November 23, 2021, per 100 inhabitants
Accessed on November 23, 2021[I]

Deaths from COVID-19 in the world

The 7-day moving average of deaths per million inhabitants, per day, is as follows:

Table 2: Number of deaths per day per million inhabitants (7-day moving average), on November 23, 2021

Accessed on November 23, 2021[ii]

Vaccination x deaths

Graph 1: Moving average (7d) of deaths per day, per million inhabitants x Vaccination, expressed in total doses per 100 inhabitants[iii]


 Vaccination x deaths: some considerations

An immediate and encouraging conclusion emerges when comparing, on November 23, 2021, the number of deaths with the level of immunization of the populations: in all countries where the threshold of at least 150 doses administered for every 100 was exceeded inhabitants – something on the order of 70% of the population with complete vaccination – the number of deaths was sharply reduced, not exceeding 2 per million inhabitants per day (moving average of 7 days), or the equivalent, in Brazil, to around 400 deaths/day. In other words, in the two dozen countries where vaccination has reached or surpassed 70% of the population, it can be seen that the number of deaths today is in the order of magnitude of 2 per million inhabitants , per day, or less than that. This is a very positive and, at the same time, tragic fact, because it means that, if the immunization process had not taken longer than it should have, we could have saved a significant number of lives in our country.

It is also verified, based on the data presented, that when the level of vaccination is lower, what is conventionally called the 'fourth wave of COVID-19' is not necessarily in progress.

To better understand the situation, from a geographic point of view, we have constructed two graphic representations below.

The first, shown in Graph 2, in which less vaccinated countries appear in a darker color (the index used here was the inverse of vaccination – see footnote, below, for the necessary details). And the second, as shown in Graph 3, in which the most impacted countries, in terms of the 7-day moving average of the number of deaths per day, per million inhabitants, also appear in a darker color.

Comparing Graph 2 with Graph 3, it is clearly seen that there is a coincidence when looking only at countries in temperate zones: the less vaccinated, the more deaths. In the case of these countries, Graph 1 shows that when vaccination is below 150 doses per 100 inhabitants – which corresponds to the labels of countries marked with yellow and red colors – the incidence of the number of deaths is inversely proportional to the number of people vaccinated .

In the tropics, however, there are places where vaccination accumulated so far is reduced and, even so, the number of deaths remains at low levels – these are the countries marked in blue, in Graph 1.

Graph 2: Inverse of vaccination (the less vaccinated, the darker)

Graph 3: Deaths, 7-day moving average of deaths per million inhabitants (the more deaths, the darker)[iv]

A more detailed analysis, however, reveals that this difference is not limited to geographic or climatic issues. There is another factor – and certainly not the only one – that is of statistical importance: it is the structure of the age pyramid in the countries under study, which can be seen by comparing those marked in red with those in blue (in Graph 1). This is what Table 3 shows.

Table 3: Vaccination, deaths and percentages of the population over 70 years old.

November 23, 2021, Source: Our World in Data, Elaboration: Gil Vicente Reis de Figueiredo


Table 3 shows that countries with low vaccination rates and, at the same time, a low number of deaths, have low percentages of elderly people (age ≥ 70 years) in their populations, around 2% – 3% of the population, while the that, under the same conditions, face the 'fourth wave', this percentage is situated in the range of 7% – 13%, therefore more than triple. It is worth noting that this differential in deaths probably also contributes to the influence of climatic factors (winter is approaching in the northern hemisphere), which lead to a greater concentration of people in closed spaces. The available data therefore show that in countries with few elderly people, the reduction in deaths is achieved with a relatively low percentage of immunization; and that, even where there are more elderly people, the number of deaths is small in those where vaccination has advanced sufficiently. It is already possible to conclude, although we must be attentive to future developments, that immunization has been playing a decisive role in reducing deaths from COVID-19.

*Gil Vicente Reis de Figueiredo is a retired professor at the Department of Mathematics at the Federal University of São Carlos (UFSCar).



[I] vaccine doses administered per 100 people, Nov 23, 2021

[ii] available from COVID-19 Data Explorer, Daily new confirmed COVID-19 deaths permillion people7-day rolling average.

[iii]Deaths on the vertical axis. Vaccination on the horizontal axis. November 23, 2021, Source: Our World in Data, Gil Vicente Reis de Figueiredo

[iv]7-day moving average of the number of deaths per day per million inhabitants. The countries analyzed are those listed in Table 1. November 23, 2021, Source: Our World in Data, Elaboration: Gil Vicente Reis de Figueiredo.


















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