For whatever reason, Oregon seems to be doing probably the best reporting on breakthroughs and results:
https://www.google.com/url?sa=t&rct=...64yU46SmEZGhha
During the week of November 21–November 27, there were 4,134 cases of COVID-19. 2,948 (71.3%)were unvaccinated and 1,186 (28.7%) were vaccine breakthrough cases. The median age of breakthrough cases was 45 years. 28 (2.4%) breakthrough cases were residents of care facilities, senior living communities or other congregate living settings. 234 (19.7%) cases were 65 or older. There were 45 (3.8%) cases aged 12-17.