According to the Treccani dictionary (just consulted) an immunized person is a person who is made immune (refractory) to a disease, while a vaccinated person is a person who has undergone vaccination: in the case of Covid, what is the relationship between these two terms? This is one of the many questions (but above all of the many misunderstandings for which we pay the dire consequences) that often characterizes common speech, but even those who provide information are sometimes “infected with the disease”.
In the following few lines we will try, briefly, to try to clarify these two terms (and the world of news that revolves around them) by relying on the most recent Italian real data available, namely the latest weekly report on the Covid epidemic. -19 of the National Institute of Health (Iss) of 10 December 2021.
It is known, since vaccines against Covid-19 have been available, that none of the vaccines produced covers the vaccinated subjects 100%: in other words, the anti-Covid vaccines on the market today do not immunize the subjects who undergo vaccination, and this characterizes all existing vaccines regardless of the number of doses taken (first, second, third…). Moreover, no vaccine has ever had such a claim: it is the information infodemic that has invested us, together with certainly other factors that are not interested in investigating here, which has led many to create an equivocal correspondence between vaccination and immunization.
Depending on the vaccine, the doses, and the distance from the time of vaccination, the ability of the vaccine to protect us from a possible Covid infection and its negative consequences changes. And here is the point: established that the vaccine does not immunize (and this in itself would say a lot about the prudent attitudes that it would still be appropriate to adopt), what is its ability to protect us from infection and its consequences?
In this contribution, we are not interested in discussing what are the arguments supported by the pro-vax and no-vax subjects in support of their positions, but we will only be concerned with putting quantitative information on the table to describe the protection that vaccines provide: it is an important information. precisely because vaccinated subjects are not immunized.
If we consider the Italian situation, and the ISS data to date are the only ones available referring to the whole national territory, the following information appears (for details see the publication cited), taking into account that from the beginning of the pandemic to 7 December 2021 5,134,508 confirmed cases and 133,689 deaths were reported to the integrated Covid-19 surveillance system, and that from the moment of the availability of vaccines and up to 7 December 2021 it appears that 100,083,572 doses (44,376. 477 first doses, 45.835.370 second / single doses and 9.871.725 third doses).
How can we measure the vaccine‘s ability to protect us from the adverse effects of the virus? The concept of “vaccine efficacy” is used, i.e. the proportion of cases (or hospitalizations, deaths …) that occur among vaccinated subjects is compared with the proportion of cases that occur among unvaccinated subjects: if the proportion of cases among vaccinated is lower than that among unvaccinated means that the vaccine is effective (as much or as little depending on how big the difference is between the two proportions). To understand (after the calculation indicated and without getting into technicalities): a vaccine efficacy equal to 90% indicates a 90% reduction in the occurrence of cases (or hospitalizations, deaths …) in the vaccinated group compared to the unvaccinated group .
In the period with prevalent circulation of the Alpha variant (i.e. from the beginning of April 2021 to the beginning of July) the vaccine efficacy in preventing Covid-19 cases was 89%, in preventing hospitalization it was 95%, in preventing hospitalization in intensive care by 97% and in preventing death by 96%.
If, on the other hand, we look at the period with prevalent circulation of the Delta variant (from the beginning of July to the data of the beginning of December 2021) the vaccine efficacy in preventing infection was 65.1%, in preventing hospitalization of 88.7 %, in preventing ICU admissions by 93.5% and in preventing deaths by 89.2%.
As can be seen from the numbers, the vaccine efficacy varies both according to the type of virus variant that is in circulation (less coverage compared to the Delta variant), and according to the health severity of the infectious phenomenon (from the simple presence of the virus up to death), but immunization is never achieved (i.e. 100% efficacy), even in the face of the most serious outcomes: some subjects, despite being vaccinated, will become infected (without other consequences) and others (much less) will unfortunately arrive to death. The report also reports differences in efficacy by age, by type of vaccination completeness (one, two, three doses) and by distance from completeness of course (less or more than five months), but we don’t have the space for details.
For the sake of completeness, since the available data do not refer to a random sample (i.e. adequately selected from a statistical point of view), but has privileged the vaccination of the population groups at greatest risk in the timeline, it should be added that the proposed results should represent an underestimation of the overall vaccine efficacy, and that the actual efficacy should therefore be higher than the reported values.
Some, limiting themselves to observing the absolute number of cases, support the thesis that the events of infection among vaccinated subjects are comparable, if not even higher, to those among unvaccinated subjects, with the obvious consequences that can be imagined. This is what is defined with the term “paradoxical effect”: when vaccinations in the population reach high levels of coverage, and therefore there are many vaccinated subjects, the absolute number of infections, hospitalizations and deaths (since vaccination efficacy is not 100%) may be similar, if not greater, between vaccinated and unvaccinated. Is called paradox effect, but in reality it is about a real comparison error, as the correct comparison must not be made between the absolute numbers of cases (between vaccinated and unvaccinated), but between the values of the respective rates (because in this way the different numerical dimensions of the populations being compared are correctly taken into account).
For example, according to the ISS Report in the last month, the hospitalization rate for the unvaccinated is 83.9 hospitalizations per 100,000, that of vaccinated individuals with a full cycle for less than five months is 7.8 hospitalizations per 100,000 (over 10 times lower), that of vaccinated with full course over five months is 16.6 hospitalizations per 100,000 (about 5 times lower), and that of vaccinated with full course + additional dose / booster is 9.8 per 100,000 (over 8 times lower); for ICU admissions, the rate for unvaccinated people is 11.4 per 100,000, that of vaccinated with a full course less than five months old is 0.7 per 100,000 (over 16 times lower), that of vaccinated with full cycle for over five months is 1.2 per 100,000 (slightly less than 10 times lower), and that of vaccinees with full cycle + additional dose / booster is 0.8 per 100,000 (14 times lower); for deaths the rate for unvaccinated is 16.6 per 100,000, that of vaccinated with a full course for less than five months is 1.5 per 100,000 (11 times lower), that of vaccinated with a full course for over five months is 2.4 per 100,000 (nearly 7 times lower), and that of full course vaccinees + additional dose / booster is 1.0 per 100,000 (over 16 times lower).
Of course, there is obviously much more that can be said about the themes and figures that have been introduced: the hope of the writer is that the proposed numbers and the information they bring with them can help readers improve their knowledge of effects of the pandemic and the tools with which it can be tackled.
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