It’s all about probabilities. Vaccinated people have less of a viral load and infect fewer people. It’s never all or nothing. Reducing the r-value even by just 0.1 compounds in huge returns in exponential growth scenarios.
https://www.ucdavis.edu/health/covid-19/news/viral-loads-sim...
Do you have other references?
Second, fewer vaccinated people have breakthrough infections in the first place, so overall spread is lowered because of vaccinations.
It does seem better, but can we know for sure to what this can be attributed? Usually places that had an easier time in 2020 got worse this year, and vice-versa, which makes sense...
Bulgaria looks like reporting is not reliable: https://www.economist.com/graphic-detail/coronavirus-excess-...
A better comparison would be Bulgaria to Portugal.