Вот тут сразу два независимых исследования это утверждают:
People vaccinated with Pfizer’s shots and who still get infected with the coronavirus carry less virus in their bodies than unvaccinated people who are infected, researchers from Israel report in two separate preliminary studies posted February 8 at
medRxiv.org.
Curious to see if the vaccination effort was curbing viral transmission, researchers compared the levels of virus in more than 15,000 coronavirus test samples. The team did not know the vaccination status of those tested. But “this was a unique point in time where we had two different groups” in the population, with older people probably having been vaccinated and younger people most likely not, says Ella Petter, a computational biologist with MyHeritage Lab, a genealogy company headquartered in Or Yehuda, Israel, that conducts COVID-19 tests.
Samples that tested positive for the coronavirus from people over age 60 had lower levels of the coronavirus on average than samples from people 40 to 60 years old, who were less likely to have been vaccinated, Petter and her colleagues found. Computational analyses showed that the vaccine rollout best explained the differences between the two groups, rather than factors like demographics or new coronavirus variants (SN: 2/5/21).
https://www.sciencenews.org/article/coronavirus-covid-19-pfizer-vaccine-may-reduce-transmission
