Vaccination makes infected less contagious

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According to a study from Israel, Sars-CoV-2-infected people reproduce fewer viruses after the first vaccination dose than unvaccinated people – and would thus be less contagious.

If people become infected with the pathogen Sars-CoV-2 after a Corona vaccination, they apparently reproduce fewer viruses than unvaccinated people – and would thus be less contagious. This is true even after a single vaccination dose, write Israeli researchers in a study that has not yet been peer-reviewed. Clemens Wendtner of the Munich Clinic Schwabing sees the result as a “cause for hope”.

It’s a key question in the current phase of the pandemic: The Corona vaccine protects people from the Covid-19 disease, but are vaccinated people also less contagious in case of infection? The team led by Idan Yelin of the Institute of Technology in Haifa investigated this question using laboratory results from a total of almost 5,800 infected people, which were subsequently analyzed. About half of the participants had received a vaccination dose with the Biontech/Pfizer preparation; the others were unvaccinated.

In those 1140 people whose vaccination had already taken place twelve to 28 days previously, the viral load determined by PCR examination was four times lower than in the unvaccinated. Wendtner emphasizes, “The BNT162b2 vaccine not only leads to individual protection of the vaccinated person with regard to Covid 19 disease, but it can be assumed that if the population is sufficiently vaccinated, a certain population protection in the sense of vaccine-based herd immunity can realistically arise.” Future studies, however, would have to show how long such an effect actually lasts.

Wendtner points to further open questions: It is unclear, for example, whether the viruses detected in the vaccinated persons were infectious at all – they could also have been non-replicable virus envelopes. Another question is how much the lower viral load of the vaccinated persons actually allows conclusions to be drawn about their infectiousness.

This is also the point for Marco Binder of the German Cancer Research Center in Heidelberg to be able to estimate the epidemiological use of mass vaccination: The possible lower infectivity is “in principle a gratifying finding,” he says. However, it remains questionable to what extent “a fourfold reduction actually has an effect on the infectiousness of the persons affected”.

In addition, it remains to be clarified how the second vaccination dose affects the viral load of infected individuals, he said. “Answering these questions will take time, but it will be indispensable to reliably assess and predict the impact of vaccination campaigns on the epidemiological situation.” Basically, Binder emphasizes, the study does not allow for a statement on “how high the proportion of vaccinated persons is in whom a subsequent infection is completely prevented.”