Re your fear regarding a vaccine side effect;
Vaccines are not a medicine. They are not drugs altering body chemistry, or designed to otherwise interfere with some specific body function.
A vaccine is designed to teach the immune system about a specific, non lethal pathogen, so that when it encounters said pathogen it is more prepared.
This concept of vaccine has been around for a Long time and is well understood.
With any vaccine it is tested primarily for effecacy (how good is it at preparing the body) and reaction (what effects does the body have to it) and as such it is short-term side effects which are of concern.
The two things that slow down vaccine research are disease prevalence (ie a big enough control group) and willingness to experiment (ie a big enough group of volunteers). It may come as no surprise that getting sufficient numbers for this study was not a huge hurdle. (there's a reason no-one signed up for trials of a new rabies vaccine, but there were thousands who signed on to covid vaccines.)
Could long term effects happen in vaccinated people? Yes, in the same way someone might be hit with a meteor. It's possible, but unlikely. On the other hand the possibility of getting covid is high, with about 15% suffering from long-covid and possible long term side effects.
We are often poor at evaluating relative risk - and we tend to favour the known (no matter how risky) compared to the unknown.
In this case though there is more data on hand than pretty much any vaccine in history, so feel free to do the math.
Lastly, yes there will be varients forever. People will likely catch covid, and die forever, just like the flu is with us now. You can't stop the dice from rolling, but you can substantially change the odds.