RIP, Colin Powell - didn't always agree with him, but at least he followed his personal convictions, rather than popularity, to be sure.
He was fully vaccinated and died of breakthrough infection.
As we know, the CDC has published data suggesting that most deaths from COVID-19 among the vaccinated are over age 80 (thus the FDA's approval of a third Pfizer booster shot for them, with Moderna's on deck for approval, and J&J's next.), and that most people younger than 80 that have been vaccinated have mild symptoms.
The CDC also has published data suggesting that Moderna's vaccine has slightly longer effectiveness (which I posted previously), and is considering allowing J&J people to be cross-vaccinated with other brand vaccines (which you may recall was another question I had in those posts about the third shot, whether we could cross-vaccinate at some point).
So, here's what we know ... that vaccine efficacy IS starting to wane, and apparently wanes over time, and that at some point, we're going to need something else - hopefully a booster with added genetic variant material, rather than the same exact formulation.
It's possible, even likely, that a third shot of the exact same formulation will at least temporarily boost immunity, it's just the small study didn't definitively prove it.
This is why we wear masks though vaccinated, people - to at least offer some physical barrier protection.