I actually got the arm rash about 8 days after the first Moderna shot. I initially thought it was from a bug bite, then I read about this being a possible reaction, especially in women. I am allergic to latex and shellfish. Took an antihistamine prior to my shot both times, just in case.
A lot of people are getting the shot done wrong. Something about pinching the muscle.
I have heard of delayed allergic reactions like that.
A friend’s daughter was on sulfa drugs for an infection.
A week after she had finished the course of sulfa, she broke out with a bad case of hives. They went to the ER and the folks there told her that sometimes that happens and not to take that again.