It happens with a lot of vaccines. Look up the 60 minutes on the 1970s Swing Flu vaccine (it's difficult to find; Google wants to memory hole it). For a lot of people, it goes away in 1~3 months, but for 3,000~4,000 people, it was permanent with the Swine Flu vaccine. There were class action law suits over it. Some people had trouble walking or issues with one side of their body (similar to stroke) for several years after. A couple of million people got it without bad effects, but you cannot discount that there is a risk. Also that vaccine: very ineffective. Vaccines should never be rushed to market. Also: we still don't know why this happens, and it's happened with multiple vaccines now. With this one, we're seeing it happen with two entirely different vaccine types (traditional/inactivated vs mRNA).