Effectiveness of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines on covid-19 related symptoms, hospital admissions, and mortality in older adults in England: test negative case-control studyBMJ 2021; 373 doi: https://doi.org/10.1136/bmj.n1088 (Published 13 May 2021) Cite this as: BMJ 2021;373:n1088
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The efficacy of a single dose of either the Pfizer vaccine or the AstraZeneca vaccine con only be rigorously evaluated if evidence of previous covid-19 infection is an exclusion criterion for subjects being evaluated. The rationale is that, among individuals previously infected with SARS-CoV-2, antibody responses to a single dose of the Pfizer vaccine are similar to those elicited by the two-dose regime(1). This implies that, in subjects who have evidence of previous SARS-CoV-2 infection, a single dose of Pfizer vaccine will suffice to provide protection against SARS-2 CoV-2 infection. By analogy that should also apply to the use of the AstraZeneca vaccine.
(1) Ebinger JE., Fert-Bober J., Printsev I et al
Antibody responses to the BNT162b2 nRNA vaccine in individuals previously infected with SARS-CoV-2
Nature Medicine https://doi.org/10.1038/s41591-021-01325-6
Competing interests: No competing interests
In this month of June, the first efficacy results of both vaccines that are in the phase III clinical trial should be known. We would like our vaccine to be 100% effective, but we know that it would not be real.
The studies that are being carried out at the moment are carried out in a scenario where other variants of the virus are already circulating in our country, such as the strain detected for the first time in South Africa and which is one of those declared as of ׳ concern׳, due to the World Health Organization (WHO), and before which it has been seen that other vaccines that already have permission for emergency use decrease their effectiveness, according to studies.
This variant of the virus does not escape the protection of this vaccine, but it does decrease its effectiveness. This means that our clinical evaluations are being carried out in a truly challenging context for our vaccine candidates.
Phase II clinical studies of Soberana 02 and Abdala have shown that the levels of protective antibodies that neutralize the virus are around 95%, that is, they induce high antibody titers. In fact, one percent of the people of around 1000 volunteers who participated in this phase hyperrespons to the vaccine with very high antibody titers.
The studies are being carried out with great rigor, the N of our trials is large, because the incidence is not that high. Even last year, in the midst of the development of vaccine candidates, the incidence was lower and at one point it was thought that we would have to go to other places to carry out efficacy studies. Unfortunately, the incidence increased, but the context allows us, with this N that was calculated, to have the efficacy results.
For several days the regulatory agency made a call and began a process to evaluate everything done in recent times - they have examined the entire process, because in order to do a Phase III they had to evaluate the results of Phases I and II—. Now all the elements that have to do with the production process are being evaluated; new information that has been provided from preclinical studies and vaccine stability studies over time.
All this information is being prepared to present it to the regulatory authority, so that when the first information on its effectiveness is obtained, the other elements have already been evaluated and an emergency use permit can be accessed in less time.
Competing interests: No competing interests
It is absolutely correct to monitor the effectiveness of the currently available anti-CoViD-19 vaccines, with particular emphasis on their ability to adequately protect immunized people from SARS-CoV-2 "variants of concern" (VOC), such as the "English" (B.1.1.7), "Brazilian" (P.1), "South African" (B.1.351), "Nigerian" (B.1.525), "Mexican" (B.1.1.222) and, especially, the scary "Indian" (B.1.617) VOC.
In this respect, a more conspicuous set of data is urgently needed regarding vaccinated (and infected) hosts' T-cell-dependent immunity in comparison to antibody-based (humoral) antiviral immunity, for which many more data are available.
Another issue of critical relevance is that, having SARS-CoV-2 caused a pandemic with 165 million cases and 3,400,000 deaths worldwide, the aforementioned vaccines should reach in the shortest amount of time as many people as possible throughout the entire globe, without leaving any Continent and/or Country behind (as it seems to be happening, unfortunately).
This is an absolute prerequisite for achieving, as soon as possible, the so-called "herd immunity" against SARS-CoV-2, where the expression "herd immunity" should be meant at the national as well as at the continental and at the planetary levels.
By doing so, the development of new, dangerous SARS-CoV-2 VOC should be markedly slowed, if not even inhibited.
Within such a complex and intricate framework, there is another element deserving additional consideration, namely the role potentially played by animals in the generation of new viral VOC.
In this respect, several domestic and wild mammalian species have been reported to be naturally and experimentally susceptible to SARS-CoV-2 infection, thereby also serving as putative animal models for a better pathogenetic characterization of the various CoViD-19 human disease phenotypes (Di Guardo, 2020).
Furthermore, beside their well-documented sensitivity to both natural and experimental infection (Shi et al., 2020), domestic cats have also been shown to suffer from SARS-CoV-2 infection due to the "English" VOC (B.1.1.7), as recently reported in North-Western Italy (Piedmont Region) in a cat which acquired the "mutated" virus from its CoViD-19-affected owners.
Still noteworthy, if not even more important, minks intensely reared in The Netherlands and in Denmark were shown, during last spring and summer (and, therefore, well before the first anti-CoViD-19 vaccines became available), to acquire SARS-CoV-2 infection from their breeders and keepers, and to "return" to them the virus, thereafter, in a "mutated" form (so-called "cluster 5").
To the best of my knowledge, mink is thus far the only species, apart from the human one, in which SARS-CoV-2, once acquired from man (so-called "spillover"), is able to undergo a series of mutational events leading to a virus subsequently re-transmitted to humans (so-called "spillback"), which is different from the one originally caught from their breeders and keepers.
In light of the above, why not consider the possibility of vaccinating animals against SARS-CoV-2, with special emphasis on those living in close contact with humans and, overall, on intensely reared animals, such as minks and pigs?
As a matter fact, by encountering more and more susceptible (and non-immunized) animal hosts along its way, the possibility that SARS-CoV-2 will continue to "mutate" - independently from human mass vaccination against CoViD-19 - should be adequately taken into account, thereby utilizing a simultaneous "One Health" and "evidence-based" approach, the former of which reminds us that human, animal and environmental health are indissolubly linked to each other.
1) Di Guardo G. (2020) - Animal models and pathogenetic insights to CoViD-19. Journal of Comparative Pathology 179: e1.
2) Shi J., et al. (2020) - Susceptibility of ferrets, cats, dogs, and other domesticated animals to SARS-coronavirus 2. Science 368: 1016-1020.
Competing interests: No competing interests