"less likely" is bureaucratic weasel language which could encompass a percentage reduction anywhere from 1 to 99 percent. But what the CDC specifically said in the Provincetown study is that "vaccinated individuals infected with delta may be able to transmit the virus as easily as those who are unvaccinated." https://www.washingtonpost.com/health/2021/07/29/cdc-mask-gu...

Also from that article: > The breakthrough cases are to be expected, the CDC briefing states, and will probably rise as a proportion of all cases because there are so many more people vaccinated now. This echoes data seen from studies in other countries, including highly vaccinated Singapore, where 75 percent of new infections reportedly occur in people who are partially and fully vaccinated.