We know some people are going to have an allergic reaction, which is why some people don't get vaccinated and it's why the protocols include a minimum of 15 minutes monitoring.
EDIT: 10 million doses have been administered.
https://www.merckmanuals.com/home/immune-disorders/allergic-...
Everyone has been pretty clear that if you have a history of the latter you should have a talk with your physician about risks and benefits.