acid reflux; distended belly and she is taking minimal (1/5) of her feeds and her stomach is distended.; eating less at feedings; fussiness and she has been throwing her neck back and thrashing to not eat; reported that his baby received an expired dose of HIB on 10-OCT-2021; baby received an expired dose of HIB on 10-OCT-2021; Initial information was regarding an unsolicited valid non serious case was received from a consumer/non-healthcare professional via Medical Information (MI) (Reference number- 00808352) and transmitted to Sanofi on 12-Oct-2021.    This case involves a two-month-old female patient (born at 32 weeks gestation) who experienced acid reflux (gastrooesophageal reflux disease), distended belly and she is taking minimal (1/5) of her feeds and her stomach is distended (gastric dilatation), eating less at feedings (poor feeding infant), fussiness and she has been throwing her neck back and thrashing to not eat (irritability), after receiving HIB (PRP/T) VACCINE [ACT-HIB] (expired vaccine used) (product administered to patient of inappropriate age).  The patient's medical history, past medical treatment(s), vaccination(s) and family history were not provided.  Concomitant medications included ROTAVIRUS VACCINE and DIPHTHERIA VACCINE TOXOID, PERTUSSIS VACCINE ACELLULAR, TETANUS VACCINE TOXOID (DTAP) for Immunisation.  On 10-Oct-2021, the patient received a first dose of suspect HIB (PRP/T) VACCINE (Powder and solvent for solution for injection, lot number and expiry date not reported) via intramuscular route in thigh (unsure which side) administration site for prophylactic vaccination.   On 10-Oct-2021, the patient developed a non-serious acid reflux (gastrooesophageal reflux disease), distended belly and she is taking minimal (1/5) of her feeds and her stomach is distended (gastric dilatation), eating less at feedings (poor feeding infant), fussiness and she has been throwing her neck back and thrashing to not eat (irritability) (on the same day) following the administration of HIB (PRP/T) VACCINE.  It was an actual medication error due to expired vaccine used and product administered to patient of inappropriate age (latency: same day).  Details of laboratory data not reported.  It was not reported if the patient received any corrective treatment for the events.  It was reported "distended belly, eating less at feedings, and fussiness. Per the caller, the baby has not been eating well since getting the vaccines. She is taking minimal (1/5) of her feeds and her stomach is distended. The baby finally pooped this morning. She has been throwing her neck back and thrashing to not eat. The parent is hoping that it is possibly acid reflux".  At time of reporting, the outcome was unknown for the events.  This suspected adverse reaction report is submitted and classified as a medication error solely and exclusively to ensure the marketing authorization holder's compliance with the requirements set out in the Directive 2001/83/EC and Module VI of the Good Pharmacovigilance Practices. The classification as a medical error is in no way intended, nor should it be interpreted or construed as an allegation or claim made by the marketing authorization holder that any third party has contributed to or is to be held liable for the occurrence of this medication error.  There will be no information available on the batch number for this case.