No vaccine can prevent transmission of a virus. Viruses go where they will. What a vaccine can do is minimize an infection cycle, and at that they're really good. When the virus invade the body it finds an already primed immune system and can't get a good foothold. That's especially important for a virus like COVID, that can infect many many different cell types. The Polio vaccine didn't immediately stop the spread of the virus. But you got a very minor disease vs. paralysis. For COVID you might get some cold symptoms, but you aren't going to the hospital.
We're in a very, very new situation that we've never been in before as a nation and as a species. We have a dangerous new virus against which we've just developed a vaccine. Immunized people can still get and transmit the virus, but they won't be badly affected by it. We haven't seen this previously because the vaccines in common use had been in common use for decades. When they were first introduced the same situation applied. Now it is far harder for the viruses to get a foothold because there are so many vaccinated people.
At least there used to be. Because of the antiscience movement which seems to garner wide support on this site lots of folks aren't vaccinated. There are routinely huge outbreaks of infectious viral disease all over the Western world. As antiscoience spreads, and it will, there will be fewer and fewer vaccinated people. And viral disease will become that much more prevalent.
The bolded statement, I do not understand. The average age of death of a covid victim is the same as the average lifespan. So collectively, it's not making a damn bit of difference in our species. Or maybe it's improving us, culling the weak. Covid is only dangerous to very old people and people who are already sick with underlying conditions. There are rare exceptions but when have we ever made sweeping policy on the outlier exceptions? Don't answer that, we do it all the time. Policy is made on the public's perception of risk, not real risk. This is why we spend $$Billions retrofitting tank cars that carry crude and ethanol to increase their jacket thickness by 1/16" even though virtually no one has been killed by tank car explosions, yet we have no problem transporting corn syrup in tanks all over the place so it can kill millions with diabetes.
Given that we had the Black Plague, how can you say we're in a dangerous new situation we've never been in before? Relative to that, we're not in any situation at all. Those people would laugh us out of town.