We keep hearing millions have safely taken the vaccine, but proof of the pudding will be how the immune system reacts when the vaccinated ..?

Yes millions have taken the vaccine which means that millions have already been exposed to the virus because there are more millions who are not vaccinated and are still spreading it. They are not becoming clickers or blobs like the video game "The last of Us" after the exposures. 

If they blew up and died after getting the vaccine the whole world would know. Nobody who got the vaccine and were exposed to the virus during the trials died. None, zero and so far nobody who has been vaccinated has died of COVID post release. None.

You're in luck - we already know what happens then.

The term you're looking for is "breakthrough cases."  That is, cases of people who are fully vaccinated, yet get the infection.

They aren't unexpected, since 99% effectiveness means we actually EXPECT 1% to still get it.

And what we see is that in those rare breakthrough cases, symptoms are much less severe than in unvaccinated people.

Everyone will turn into brain-eating zombies.

I'm not worried though as the zombies will starve to death at my house.