Adacel was mixed with 0.5 ml of sterile diluent and administered to a patient in error with no reported adverse event; Initial information received on 21-Jan-2025 regarding an unsolicited valid non-serious case received from a other health professional. This case involves an unknown age and unknown gender patient to whom had administered Diphtheria-2/Tetanus/5 AC Pertussis Vaccine [Adacel] was mixed with 0.5 ml of sterile diluent and administered to a patient in error with no reported adverse event. The patient’s past medical history, medical treatment(s), vaccination(s) and family history were not provided. On an unknown date, the patient received a unknown dose of suspect Diphtheria-2/Tetanus/5 AC Pertussis Vaccine Suspension for injection (strength: unknown, expiry date: 01-Feb-2026, lot 3CA17C1) via unknown route in unknown administration site as immunization and was mixed with 0.5 ml of sterile diluent and administered to a patient in error with no reported adverse event (product preparation error) (same day latency). 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.