Thursday, February 2, 2023
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Fundamental Science: Why criticisms of Covid vaccines are baseless


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Recently, arguments have resurfaced about the uselessness of vaccines for transmitting the Covid-19 virus. Critics have claimed that Pfizer-BioNtech got the vaccine approved without assessing the impact on virus transmission, but this is untrue. It is important to remember that, at the beginning of the clinical trials of the immunizer developed by the pharmaceutical company, the main objective was to find out if it would be able to reduce the risks of symptomatic infection, in addition to death from the disease. And that was done: Pfizer-BioNtech delivered a medication that fulfilled what it set out to investigate in clinical trials.

So much so that the approval of this vaccine was positively received by regulatory agencies around the world, such as the European Medicines Agency, in 2020. When authorizing the use of the Pfizer vaccine, she reinforced that “the excellent effectiveness of the vaccine (preventing Covid -19 symptomatic) had been demonstrated in individuals with no evidence of prior SARS-CoV-2 infection”.

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However, the agency reinforced that “it was not known whether or not the vaccine would protect against asymptomatic infections or what would be its impact on viral transmission”. Therefore, if since 2020 we had information about what was and what was not investigated at the time of clinical trials, we must not allow scientific information to be interpreted with biases that generate undue uncertainty.

With the pandemic, the world witnessed, in real time, the process of research, production and licensing of vaccines in different parts of the world, using the most diverse technologies. We also tracked how regulatory health agencies evaluated requests for emergency use and full use. The success of vaccination campaigns requires that they make clear to the population the benefits of immunization, encouraging their adherence. Actions in the opposite direction have a high cost in lost lives.

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According to a document from the European Center for Disease Prevention and Control (ECDC), the “four potential objectives of vaccination against Covid-19 are: reducing pressure on the health system; reducing severity and overall mortality; reopening society and disease elimination”. If we look at the clinical studies (divided into phases that include safety assessment, immune response induced by vaccination and vaccine efficacy in a population sample), we will see that, in the case of the vaccine developed by Pfizer and BioNTech, the primary objective was to investigate the safety and protection against symptomatic Covid-19, followed by the investigation of protection against its most severe manifestation.

It is clear that, from the detailed study protocol of this vaccine (published in November 2022), the understanding that the research was proposed to evaluate the effectiveness in reducing risks for the disease caused by Covid-19 is reinforced. The criticisms are therefore unfounded.

Other pharmaceutical companies also developed immunizers against the same disease and followed similar primary objectives. Astrazeneca (which in Brazil conducted clinical studies in partnership with the Oswaldo Cruz Foundation), for example, investigated the safety and efficacy “in preventing the onset of symptomatic and severe Covid-19 disease”, according to the publication of its study of phase three. In parallel, the same pharmaceutical company (in partnership with Sinovac) conducted a clinical study whose main objectives were also safety and efficacy in protecting against symptomatic cases, and, secondarily, efficacy in protecting against severe disease.

This logic also differed from other clinical trials, such as those carried out by pharmaceutical companies CanSino, Janssen and Novavax. Although they have not tested the effectiveness of the immunizer against the transmission of the virus, this does not mean that it cannot have effects on its spread.

After the approval of these immunizers, their impact among vaccinated and unvaccinated people was investigated. A study published in 2022 evaluated individuals who received Pfizer / BioNTech and AstraZeneca immunizers and demonstrated that ′′ vaccination was associated with a reduction in transmission ′′ of SARS-CoV-2 variants, such as Delta. According to the Centers for Disease Control and Prevention (CDC) website, “Substantial reductions in SARS-CoV-2 infections (both symptomatic and asymptomatic) will reduce overall disease levels and therefore transmission of the SARS-CoV-2 virus. CoV-2 in the United States”. Another study published in 2022, carried out in Israel, demonstrated that the Pfizer and BioNTech vaccine is capable of reducing home transmission of the Covid-19 virus.

Vaccines are not 100% effective in preventing the disease, and we know that immunized people can transmit the virus. The key issue, however, is that a vaccinated population transmits at significantly lower levels than an unvaccinated population, and as vaccination uptake increases, there will be even greater impacts on virus transmission. This is also observed in current contexts, with the predominance of the Omicron variant, as shown in this Nature publication. With the appearance of variants of the new coronavirus, presenting characteristics of greater transmissibility and partial evasion of the immune response, it is even more necessary to raise awareness in favor of vaccination, especially in updating the vaccination schedule with boosters.

It is thanks to the effects of vaccination that we observe a lower risk for severe conditions caused by SARS-CoV-2 and we observe the indirect effects that result in benefits shared by the entire population. If we add to this society’s awareness of behaviors that reduce the risk of exposure in different contexts, we see how vaccines contribute to the resumption of various activities without generating a significant increase in the number of new cases. Vaccination is part of the history and health of Brazilians, it freed us from terrible diseases that, in the past, were part of our reality, and today it helps us to deal with new emergencies that one day will also be part of the past.


Mellanie Fontes-Dutra, biomedical doctor, professor at UNISINOS and coordinator of Rede Análise.

Lorena Barberia, political scientist, scientific coordinator of the Solidarity Research Network in Public Policies & Society and member of the COVID-19 BR Observatory.

Roberto Kraenkel, physicist, full professor at the Institute of Theoretical Physics at UNESP and member of the Covid-19 BR Observatory.

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