"Remains unclear" is very different from "no impact on transmission rates". Here's the follow-up paper from the same group [1]
> These results suggest that the vaccine is initially effective in reducing infectiousness of breakthrough infections even with the Delta variant, and that while this protectiveness effect declines with time it can be restored, at least temporarily, with a booster vaccine.
The paper you're looking at is analyzing waning immunity against the Delta variant.
> These results suggest that the vaccine is initially effective in reducing infectiousness of breakthrough infections even with the Delta variant, and that while this protectiveness effect declines with time it can be restored, at least temporarily, with a booster vaccine.
The paper you're looking at is analyzing waning immunity against the Delta variant.
[1] https://www.medrxiv.org/content/10.1101/2021.08.29.21262798v...