Science uses statistics.
That means that something that is great for some people is dangerous for others.
When you don’t do the long term studies (years, large populations) there is no reliable way to determine who falls into what category.
That turns medicine into Russian Roulette.
Statistically speaking, the vaccine is perfectly safe. I just vaccinated 14 people with dose 2. They were all fine. I’m clocking in right now to vaccinate another 100 tonight.