Readers’ Letters: Vaccines and Transmission of COVID-19

The article « Will Covid-19 stop being transmitted thanks to vaccines? »[Smriti Mallapaty; Research and Science , April 2021] addresses the question of the extent to which vaccination will prevent the spread of SARS-CoV-2. It states that “preliminary analyzes suggest that some vaccines are likely to be able to stop the transmission of the virus. But it is not easy to confirm this effect or its forcefulness, because a fall in infections in a given region could be explained by other factors, such as confinements and changes in customs. Furthermore, as asymptomatic carriers also spread the virus, the detection of such infections is very difficult. ‘

The author includes the opinion of several experts and mentions the clinical trials carried out to evaluate the vaccines, as well as the intention of Pfizer to start doing swabs to see if their injections can block the infection. Studies are also pointed out that suggest that the viral load after vaccination “is a good indication of contagiousness” and two bibliographic citations are included, one from February 2 and another from February 8, 2021, which reinforce the opinions expressed in Article.

In this regard, it is interesting to note that, a few days after the original version of Mallapaty’s article appeared in the journal Nature , Noa Dagan, of the Clalit Research Institute, and her collaborators published in The New England Journal of Medicine a study evaluating the results of the vaccination campaign in Israel. This study included some 1,200,000 people separated into two groups, one of 600,000 unvaccinated individuals and another of 600,000 people who had received the two doses of the vaccine. From the results it can be inferred that those vaccinated with Pfizer’s mRNA vaccine would reduce their contagion capacity by 92 percent.

Of course, it is a single study, so we will have to wait for its results to be confirmed by other studies. However, it is a very robust trial and possibly the largest and best planned to date.

Justo Aznar
Bioethics Observatory
Catholic University of Valencia

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 Research and Science content   on the COVID-19 pandemic. You can also access the articles published by  Scientific American  and other of its international editions through  this website .