By Rodrigo Ibarrola
In the comments on the daily reports of the Ministry of Health and Public Welfare (MOHPW) on the progress of COVID-19, there are often those who, based on the data, consider the vaccines are not working. If one takes a crude look at the data presented, one gets the impression that those who are vaccinated die in a proportion close to those who are not vaccinated or who have incomplete vaccination schedules. Under this simplified criterion of nominal values, the death curve would have the appearance of Graph 1.
Graph 1. Daily COVID-19 deaths, by vaccination status, year 2022, as of February 10.
Source: Own, with data from the Ministry of Health and Social Welfare (MSPBS). Note: 2022 is used because at this point is when a new wave starts and there is a relevant amount of immunized people that allows to evaluate the efficacy.
Given that the unvaccinated represent most of the population, 57%, it would seem logical that, in absolute terms, the deaths in this condition are more numerous. This logic would therefore give the impression of supporting the idea that vaccines do not make a great difference.
But this comparison has a problem when it comes to measuring vaccine efficacy. On the one hand, the population does not have a homogeneous age nor does it have the same number of people in each age group. We know that health complications increase with age and, consequently, the risk of death. On the other hand, not all age groups have the same vaccination coverage. In view of this, it is necessary to adjust for age and vaccination, what we normally call “controlling variables” for a better comparison. This is nothing more than homogenizing the size of the age groups to make them comparable. It is true, there are also other factors (comorbidities, income level, health personnel, indigenous peoples, geographic areas, etc.), but for simplicity, we resort to those reported daily by the health authorities.
For this reason, we disaggregated the number of deaths by vaccination status and by age group during a given period. Then, we grouped people with a single dose with those who were not vaccinated, since complete protection is acquired with the full schedule and, even if they have it, the new protocol establishes the need for a booster shot at six months. The results of the calculations are shown in Table 1.
Table 1. COVID-19 deaths, absolute values by age range and vaccination status, as of 10/02/22.
Source: Own elaboration with data from the Ministry of Health and Social Welfare (MSPBS).
Next, it must be equated to several comparable persons, say, per 100,000 inhabitants, in a similar situation by age range and vaccination status -again- to have it correctly adjusted by age, which results in Graph 2.
Graph 2. COVID-19 deaths per 100 000 population, by vaccination status, age-adjusted, year 2022, as of February 13.
Source: Own, with data from the Ministry of Health and Social Welfare (MSPBS).
What this result shows us is that, after adjusting for age, in general, the unvaccinated or incompletely vaccinated die six times more often (395.6/64.1=6.2) than those with the complete vaccination schedule or, in other words, complete vaccination prevents death from COVID-19 by 82%. When divided by age group, the situation is like the general situation in the 60 years and older age group. In the 40 to 59 years age group, the risk of dying if not fully vaccinated is 3.6 times higher, i.e., the vaccine prevents the fatal outcome by 74%. The gap narrows as age decreases. Thus, among those aged 20 to 39 years, the risk is 2.4 times higher, i.e., the vaccine reduces the risk by 60%. This is logical, since the youngest are the least likely to develop mild disease. Finally, the trend is reversed in the 0-19 age range; however, the data on deaths are insufficient for a meaningful assessment.
Now, given this adjustment exercise, what should the proportion of deaths be like to consider that the vaccine does not make much difference in preventing deaths? Let us take the 60 years and older age group, where 80% of deaths are grouped. Given that 74% of those vaccinated in this age group are fully vaccinated, the proportion of deaths among those vaccinated should be triple that of the other group. This is clearly not the case.
But why has confidence in vaccination been lost to the point of doubting its efficacy? We can try to come up with some answers, which are always insufficient. It may have been necessary to explain more clearly that 90% effectiveness was not an index of the probability of dying from the disease, but a ratio between the deaths among the vaccinated participants and the control group (those who received placebos). Yes, there were also deaths among those vaccinated in the trials. Or, the implications of the new variants on the initial effectiveness were not emphasized. For example, Omicron has severely subverted the efficacy of the vaccines. Recall that most vaccine trials at the time of development were conducted during the circulation of the original variable, so effectiveness (the term used in trials) is not the same as efficacy (the term used when used in populations, i.e., in the real world). Trials are not conducted in the same populations, nor at the same stage of the pandemic, nor with the same circulating variants. Everything is changeable, and so is efficacy. But that does not make it any less useful. On the contrary.
the unvaccinated or incompletely vaccinated die six times more often (395.6/64.1=6.2) than those with the complete vaccination schedule or, in other words, complete vaccination prevents death from COVID-19 by 82%
Unlike the previous calculation, where we consider the general population, if we take only those infected (Graph 3), we will see that the difference is even greater. The unvaccinated infected die 10 times more often than the vaccinated, i.e., vaccines reduce the risk of death by 91% once infected.
Figure 3. COVID-19 deaths per 1000 infected, by vaccination status, age-adjusted, Jan. 2022*
Source: Directorate of Health Surveillance, Ministry of Public Health and Social Welfare.
Vaccines do work, and the numbers bear this out.
Cover illustration: free_pik
*TRADUCCIÓN DEL GRÁFICO:
Non vaccinated
Vaccinated with one dose
Vaccinated with two doses