If you look at all of the recent CDC craziness re what the vaccinated can and cannot do from the perspective of the CDC knows that vaccines don’t really work well, they make a lot more sense.
Well, for one thing, people have this idea that vaccines are supposed to be 100% (or close to it) effective in granting you immunity, and immunity that lasts a decade or more. After all, most of the vaccines that older people got when we were younger were like that. But apparently that is only true for vaccines that use a live-attenuated (weakened version) virus, and the other types of vaccines that are more common now never work as effectively.
So even if they got these vaccines working properly, all the different versions, without proper testing, they still would expect them to only give something like 50-70% immunity, not 100% immunity, and it would last for a much shorter period of time. The CDC and all the doctors know that, even if the public has this general misconception.
On top of that, they also must know about the nature of coronaviruses, that they are fast-mutating viruses we have never had any real success vaccinating against, even if they don’t want to admit that to the public. So I think they know, even in the best case scenario, if 100% of the people were vaccinated, it wouldn’t completely stop the virus, only slow it down, and only if we get very lucky and some other variant doesn’t start spreading more successfully than the one we designed the vaccine against.