I had little bit of a rash on my arm and back; might be some shrimp ate or the shrimp crostini that I ate the night before/could be a reaction to the shrimp maybe it was not fully cooked; This is a spontaneous report from a contactable consumer (patient). A patient of unspecified age received first dose of bnt162b2 (PFIZER-BIONTECH COVID-19 VACCINE, formulation: solution for injection, lot number was EN6200, and expiration date was not reported), via an unspecified route of administration on 24Feb2021 as single dose for covid-19 immunization. Patient medical history and concomitant medications was not reported. The patient took first dose on 24Feb2021 did not feel a thing, everything was great, not any kind of symptoms or anything. On an unspecified date in Mar2021, on 10 day the patient felt like if the patient had little bit of a rash on arm and back but, patient was concerned if it could have been an effect with the first dose of vaccine or might be some shrimp ate or the shrimp crostini that I ate the night before so did not pay attention to it then on the second vaccine. The patient went to get the second vaccine, that was on the 17Mar2021, so had a little bit of the rash on the arm. The patient mentioned it to the nurse and then she said do you want to tell your doctor first before having the second dose and then I said oh no, no of course not, I said I am not going to let the little, tiny rash get in the way of getting the second dose of the vaccine. So, then I had the second dose and then coincidentally or not but the rash that I have on my back became like more intense like itchy and both arms and my back. I do not have it on the lower body it just kind of like on my lower neck, my lower back and both arms, that's kind of very itchy, so then I went to the urgent care centre on Sunday and then the doctor gave me 3 medications including the one that was called Prednisone 10 mg, so this was steroid. Then when I spoke with my doctor on Monday afternoon, he told me that he was very concerned, he told me to stop taking Prednisone (Captured suspect conservatively) right away. He said this was steroid and it could potentially block the effect or the effectiveness of the vaccine, so I don't advise to take steroid at all. So now my concern is the following, could I have potentially slow or blocked the effectiveness of the vaccine. I started taking the steroid or Prednisone, it was 4 days after the second dose of Pfizer vaccine, so I had my second dose on the 17Mar2021 around 15:30 in the afternoon and I took 10 mg of Prednisone on Sunday afternoon, so it would have been exactly 4 days after the second dose. So then on Monday morning at 9:30 in the morning I took 1 Prednisone another one at 14:30. So a total of 3 that would have been a total of 30 mg in 2 consecutive days until I spoke with the doctor in the afternoon or the evening of Monday night, and he told me stop taking it, he said I don't want you to take any chances of you blocking the effectiveness of the vaccine and then you having to maybe another boost of the vaccine or having to redo all over again, I am not taking it. But then the reason I waited hours to speak with you, is that now I am concerned, should I be worried that maybe taking those 3 pills of the steroid Prednisone, should I be concerned that maybe the effectiveness of the vaccine was not going to be like full effect like normally what it would have done without the steroid or am I safe. The patient thought that it could be something else, it could have been, because it was 10 days later, it could have been because I ate the shrimp crostini the night before and maybe it could be a reaction to the shrimp maybe it was not fully cooked. Outcome of events was unknown.  No follow-up attempts are possible. No further information is expected.