No additional AE/PQC; HCP called to report that MMR II and VARIVAX were inadvertently reconstituted with the diluent for HIBRIX (0.9% NaCl) instead of the Merck diluent provided and administered to the same patient on the same day. No symptoms reported. No further inform; This spontaneous report was received from a other health professional referred to a patient of unknown age and gender. No patient’s pertinent medical history, concurrent conditions, drug reactions or allergies, nor concomitant therapies were reported. On 27-JAN-2025, the patient was vaccinated with measles, mumps, and rubella (wistar ra 27-3) virus vaccine, live(M-M-R II) dose 1, 0.5 milliliter, intramuscular (strength, anatomical location, vaccination scheme, lot number and expiration date were not reported), for prophylaxis. On the same date, the patient was vaccinated with her/his first dose of varicella virus vaccine live (oka/merck)(VARIVAX), 0.5 milliliter, intramuscular (strength, anatomical location, vaccination scheme, lot number and expiration date were not reported), for prophylaxis. Both vaccines were inadvertently reconstituted with sodium chloride (Manufacture Unknown) diluent for Haemophilus influenzae type b. (HIBERIX) (also reported as “HIBRIX” conflicting information), (product preparation error). No adverse event was reported. Lot number is being requested and will be submitted if received.