HCP called to report that MMR II and VARIVAX were inadvertently reconstituted with PEDVAXHIB instead of the STERILE DILUENT, and administered to the same patient. HCP stated this occurred between January 7, 2025 and January 13, 2025. Exact date was; No adverse effects were reported; HCP called to report that MMR II and VARIVAX were inadvertently reconstituted with PEDVAXHIB instead of the STERILE DILUENT, and administered to the same patient. HCP stated this occurred between January 7, 2025 and January 13, 2025. Exact date was; This spontaneous report was received from a nurse regarding a 12-month-old male patient. The patient’s medical history, historical drugs, known drug allergies, concurrent conditions, and concomitant therapies were not reported. On an unknown date in January 2025 (reported as between 07-JAN-2025 and 13-JAN-2025), the patient was vaccinated with a dose of measles, mumps, and rubella (wistar ra 27-3) virus vaccine, live, recombinant human albumin (rHA) (M-M-R II) injection, 0.5 milliliter, lot #x024178, expiration date: 14-JUL-2025, and a dose of varicella virus vaccine live (oka/merck) (VARIVAX) injection, 0.5 milliliter, lot #y004554, expiration date: 20-FEB-2026 (strengths, doses, anatomical locations, and routes of administration were not reported), that were accidentally reconstituted with haemophilus b conjugate vaccine (meningococcal protein conjugate) (LIQUID PEDVAXHIB) intramuscular injection, 0.5 milliliter (strength, lot #, expiry date, and route of administration were not provided) instead of sterile diluent; all were given as prophylaxis (Product preparation error) (Wrong product administered). No adverse effects were reported. Lot # was being requested and will be submitted if received.