Seems like that is also up for debate. In this CDC study[1], 74% of cases were in the vaccinated. Probably around 69% of the population were vaccinated, meaning the fact that more than 69% of the cases were in the vaccinated suggests that the vaccinated were even more susceptible than the unvaccinated. I'm sure there are plenty of considerations with this study, but it certainly isn't glaringly obvious that vaccination reduces susceptibility.

[1]https://www.cdc.gov/mmwr/volumes/70/wr/mm7031e2.htm?s_cid=mm...