I also had a nasty reaction to the covid vaccines, but it was a lot better than if I had gotten covid. I'd rather have my wonky immune system ramp up than get extremely ill. I'm old enough that I had measles. Most vaccines in "the old days" were based on weakened bacteria or virus that couldn't infect us. The mRNA vaccines are proteins or other pieces of the bacteria or virus that are used to trigger our immune systems to attack the "real" invaders. There is a lot of research now on covid and associated reactions to infection, and vaccines. There is also a huge amount of misinformation on it (vaccines do not cause autism, bleach and dewormer don't work). Research takes time, which occurs during and following the pandemic. Some people refused the covid vaccine because "it came out too soon" (but after millions worldwide had already died), however, the vaccine was based on decades of genetic research and collaboration across countries. Are there a lot of unknowns about covid and the vaccine? Of course.