From the days of 18th century Small Pox vaccinations, when a pustule on an actively infected person was pierced and the needle put into someone else’s arm, a percentage of people receiving vaccinations become ill and even die. It’s a bit of a lottery. Personally, I’ll decline any vaccination for Covid-19 and trust to take on immunity the natural way, living life as close to normal as possible. Seems a decent bet with a sub 10% symptomatic, and below 1% death rate, virus. Contrary to the panic mongers, this isn’t like the Black Death or Yellow fever.
About 1 case per 1 million vaccines given in the past 30 years has been able to demonstrate a reasonable argument that a vaccine did any level of harm to them. That’s the payout rate from the National Vaccine Injury Compensation Program, which exists to compensate anyone injured by a vaccine. The threshold to get a payout does NOT require any medical evidence or any proof that a vaccine harmed you. It only requires a reasonable argument linking a vaccine to some sort of injury. And with that low threshold, about 1 case of compensation is provided per 1 million vaccinations.
In other words, they’re pretty darn safe and a whole lot safer than getting polio or measles or COVID-19.