This case was reported by a consumer via call center representative and described the occurrence of fever in a 12-week-old male patient who received PEDIARIX for prophylaxis. Concurrent medical conditions included gastroesophageal reflux (diagnosed when patient was three weeks of age.) and milk allergy. Concomitant products included CARAFATE and PREVACID. On 16th October 2018, the patient received the 1st dose of PEDIARIX. In October 2018, less than a day after receiving PEDIARIX, the patient experienced fever, esophageal reflux aggravated, appetite impaired, injection site warmth, injection site induration, injection site pain, mucous diarrhea, injection site swelling and feeling of warmth. On 22nd October 2018, the patient experienced lymphocyte count increased, viral infection, granulocyte count decreased and monocyte count decreased. On an unknown date, the outcome of the fever, esophageal reflux aggravated, appetite impaired, injection site warmth, injection site induration, lymphocyte count increased, injection site pain, viral infection, granulocyte count decreased, monocyte count decreased, mucous diarrhea, injection site swelling and feeling of warmth were unknown. It was unknown if the reporter considered the fever, esophageal reflux aggravated, appetite impaired, injection site warmth, injection site induration, lymphocyte count increased, injection site pain, viral infection, granulocyte count decreased, monocyte count decreased, mucous diarrhea, injection site swelling and feeling of warmth to be related to PEDIARIX. Additional details were reported as follows: The reporter's son had a history of gastroesophageal reflux that was diagnosed when he was three weeks of age. It was well controlled with medication. The morning after receiving the PEDIARIX vaccine he had a temperature of 99.4 degrees. His reflux started acting up, and he was not eating well. When the reporter went to change his son's diaper that afternoon, the injection site on his leg was hot, hard, swollen, and painful to the touch. A few hours after that, he had watery diarrhea with mucus. The injection site continued to get harder and more swollen. The reporter took him to the doctor that night and she was told to put cold compresses on the injection site 4-5 times a day and come back in two days. On 19th October 2018, the patient continued to have all symptoms, however the leg got better by Friday, when she went back to the physician. The diarrhea was not as watery but was still very mucus. Less than a week after receiving PEDIARIX, the patients temperature had fluctuated up and down, sometimes he felt warm and sometimes not. On 22nd October 2018, the reporter took him back to the physician on Monday, because there was so much mucus. Six days after receiving PEDIARIX, the physician completed blood work and it was noted that his granulocytes were low, lymphocytes high, monocytes low, and other lymphocytes high. The physician told the reporter that her son had a virus. The physician referred the patient to the gastroenterologist. The gastroenterologist told the reporter that her son's symptoms were due to the PEDIARIX. Lab Comments: On 22nd October 2018, the physician completed blood work and it was noted that his granulocytes are low, lymphocytes high, monocytes low, and other lymphocytes high.