I do not recall the vaccine mfgr’s ever stating the vaccines would give strong protection against infection.
And, even if the vaccines did give good protection against infection by “original” COVID, and we had 80% of the population fully vaccinated or otherwise immune, Delta’s virion levels in nasal passages would (or will) in fairly short order infect the 20% vulnerable. That more than explains the current numbers of cases, esp. given that very little real mitigation is occurring in most areas.
CDC’s hopelessly bad public “education” effort has not helped, either.