Biontech vaccine prevents infection by up to 90 percent

Good news from Israel: the vaccine not only provides a high level of protection against disease, but also against the transmission of Sars-CoV-2

It’s been the big sticking point since the first Corona vaccines were approved: how well can they prevent transmission of Sars-CoV-2? The clinical trials were focused entirely on the question of how well the vaccines protect against disease with covid-19 – and they do, to a very high degree of up to 95 percent. However, it remained unclear whether vaccinated people could nevertheless pass on the virus in the form of unnoticed asymptomatic infections.

In the worst case, some feared, vaccinated people could become carriers of the virus on a large scale, since they would not notice that they were infected but not ill.

Doubts about transmission protection
The experts’ estimates were originally rather pessimistic: since the vaccination is administered in the upper arm, immunization starts there. And that could be unfavorable in that the entry point of the virus is the throat and pharynx, where pathogens could possibly settle and multiply despite vaccination. Even Biontech CEO Uğur Şahin therefore considered a reduction in transmission of “only” around 60 percent to be realistic.

But now preliminary figures from Israel have become known that are even more encouraging. There, about a third of the population has already been vaccinated with two doses, and therefore, for the first time, large study numbers there can be used to determine in real time how the vaccine is working and influencing the pandemic.

Data from 1.7 million vaccinated people
Apparently, the new study, which has not yet been published, included data from around 1.7 million vaccinated people. It showed, according to consistent press reports, that the vaccine was 89.4 percent effective in preventing Sars-CoV-2 infections. Specifically, these were mainly (prevented) infections with the British virus variant B.1.1.7, which already dominated during the study with 81 percent of cases.

While only 1842 Sars-CoV-2 infections occurred in the group of those who had already received two doses of vaccination (specifically, 11.5 infections per 100,000 person-days), there were 76,797 infections in the control group of the unvaccinated, which is about ten times the rate (of 114.4 infections per 100,000 person-days).

Confirmation by British data
Admittedly, the data are only preliminary and have not (yet) been officially confirmed by Biontech/Pfizer. The associated study is currently only circulating as a 22-page paper and must first be uploaded to one of the preprint servers before it can be considered for publication in a specialist journal.

From a purely methodological point of view, however, it is not easy to measure the reduction in the infection rate through vaccination, as epidemiologist Marc Lipsich explains in the journal Nature. Because a decrease in a certain region can of course also be due to other measures such as lockdowns or behavioral changes.

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