Vaccines reduce ones chance of acquiring a Delta infection by a significant margin (not as high as previous variants but still significant). Even if you assume just 50% effectiveness in preventing disease (which is very conservative), that dramatically lowers the R-value and slows spread.
> Vaccines clearly reduce ones chance of acquiring a COVID infection by a significant margin.
All of that data is pre-Delta. The best thing you can say about the vaccines today is that they tend to reduce the overall severity/prevent people from dying.
The absolute lowest bound estimate was an Israeli study:
> In late July, the ministry further reduced its vaccine effectiveness estimate for symptomatic COVID-19 to 40.5%
However, they have failed to provide the data necessary to evaluate their results, and so at this time there's pretty wide skepticism regarding this figure.
In contrast:
> A study published in the New England Journal of Medicine on July 21 by Public Health England, for example, found that after the two recommended doses, the effectiveness of the Pfizer/BioNTech vaccine in preventing symptomatic disease in the U.K. fell only slightly, to 88.0% against delta
Being a betting man, I'd say the truth lies somewhere in the middle, but even at 60-70% effectiveness in preventing symptomatic Delta infection, vaccination leads to a significant reduction in R-value.
