A 77 year old male patient came in requesting a Hepatitis A vaccination due to the recent outbreak on 5/16/18. He and his wife came into the consultation room together, at approximately 12:15 PM. I gave him the HAVRIX shot intramuscularly into his left deltoid muscle. He bled slightly after removing the needle, and I quickly went to wipe it away with some gauze. At that point, no less than 10 seconds later, I noticed a lump in his arm that I did not recall seeing earlier. I kept watching it, to see if it was just a normal part of his arm, or if it was swelling from the shot. He noticed me looking and said 'what is that? that bump normally isn't there'. I told him that it might just be local swelling from the injection. But it quickly became apparent that it was progressing rapidly and was not a normal swelling reaction. In about 1 minute it went from a raised area the size of a quarter, to the size of a baseball, at least a half inch high. It also was covered in hives. This entire reaction took place in less than 2 minutes after giving him the injection. The patient was starting to panic stating "What happened? What did that shot do to me? That bump is not supposed to be there!" I immediately told him that it looked like he was having an allergic reaction to the shot and I did not hesitate in giving him an EPI-PEN shot, in his left thigh, through his jeans. I explained what the EPI-PEN was for and that I needed to monitor him further.  I called for help from the other pharmacist, to get BENADRYL and to call 911. She agreed that we needed further help to manage the patient. The patient began complaining of feeling unwell and breathing strangely. He also stated that his heart was racing. I explained that this may be side effects of the epinephrine. He refused to take the BENADRYL at that time because he stated he felt unwell. He still refused after I explained the purpose. The store leadership and loss prevention came to the scene quickly and assessed the situation. The patient did not want us to call 911 but the wife stated she agreed that it was needed. While waiting for 911 to arrive, we discussed the patient's previous experience with vaccinations, he never had an issue before, and gets all recommended vaccinations. It is possible because of his age that he had never had the hepatitis A shot in the past because it was not a routine vaccination until after he was an adult. I asked if he had allergies and the only one he had was a latex allergy. I assured him that the gloves I was using were latex-free. I also asked what happened and how he found out about the allergy. They said that it had happened long ago - they had forgotten the reaction and it was something that happened when he was having a surgery on his prostate. The paramedics arrived and got a history of the situation, as well as his vital signs. By the time they had arrived, significant improvement was seen in his swelling. It had decreased to only a quarter inch thickness, but still baseball size. He had a slightly increased blood pressure, normal pulse, and normal oxygen levels. The EMTs stated they felt comfortable not taking him to the hospital if the patient did not want to. They just said that he should take BENADRYL for a day or two because the EPI-PEN is just a quick fix that will wear off. After the paramedics had him sign a form saying he declined further treatment, I stayed in the room with the patient and his wife a bit longer. I explained what they should watch out for and to call with any questions, to not hesitate to call 911, and where to buy BENADRYL and how to take it. When he left, the swelling was minimal, only the size of a half-dollar.