You're right, it's partially that and partially the fact that you need two doses and potentially 2 weeks or more after the second dose to hit that 95% effective

You're right, it's partially that and partially the fact that you need two doses and potentially 2 weeks or more after the second dose to hit that 95% effectiveness. I was more responding to the idea that "maybe the vaccine isn't effective at all" which it seemed like the poster above might have been hinting at. Which doesn't make a lot of sense, because the article they linked pretty clearly lays out the rationale.