I am ignorant as hell when it comes to vaccine research and production. But I'm not dumb.
The only way this shit even gets to market, where you- the average person- can walk into a CVS and get stabby-stabbed with a needle, as if the producers of the vaccine have gone through all of the testing required by all relevant oversight committees, and just general ethics codes and observational skills, to get it rubber stamped. The overwhelming majority of people are not going to die or even suffer serious side effects from this, because such side effects would've been hashed out during the testing phase before it is approved for mass consumption. Like, they would've seen test subjects dropping like flies, gone "Oh, that's neat," and just fixed it, then tested it again, and they do this over and over until it just fucking works. Like, do you really think this thing is going to cause immediate spewing of blood from every oriface the moment it's injected, that the literal tens of thousands of people who they've already tested it on wouldn't have had that symptom pop up, and you just happen to be the unlucky one who's a unique case study?
The worst that probably happens to you is a mild immune response- fever, aches, chills etc., like with the flu shot (which just means the vaccine is actually doing its job and making sweet little antibodies)- or that it just doesn't do anything for you, since it's only 95% effective, and not 100% effective.
This is like if Ford announced a bangin' new Focus for 2022, and people who are interested in the new Focus came along and asked "How do I REALLY know the Ford Focus 2022 is going to not have the engine fall out when I drive it off the lot? I don't wanna be the first sucker!" I mean, fuck me. I dunno how car production works. I just place faith in the systems that be that Ford has to abide by- as well as the belief that they don't want the PR nightmare of explaining such a dangerous bug- to do everything physically possible to prevent the engine from falling out. Does that mean it's 100% impossible for a car engine to not fall out from a new car? Of course not. But I have driven many a car in my lifetime, and have seen tens of thousands more cars, and I haven't seen an engine fall out yet. PRETTY SAFE TO ERR ON THE SIDE OF CAUTION THAT YOUR NEW CAR ENGINE WON'T FALL OUT, AND YOU CAN BUY THAT NEW BANGIN' FORD FOCUS 2022.