administered a dose of Pentacel to a patient IM in the left thigh, also administered (in error) a dose of Daptacel to the same patient at the same time IM in the right thigh with no reported adverse event; Initial information was received on 05-Jan-2022 regarding an unsolicited valid non-serious case received from a other health professional via call center.  This case involves a 15 months old male patient who had experienced an event administered a dose of Pentacel to a patient intramuscularly  in the left thigh, also administered (in error) a dose of Daptacel to the same patient at the same time intramuscularly  in the right thigh with no reported adverse event while receiving vaccines DIPHTHERIA/TETANUS/5 HYBRID AC PERTUSSIS/IPV(MRC5)/HIB(PRP/T) VACCINE [PENTACEL] and DIPHTHERIA-15/TETANUS/5 AC PERTUSSIS VACCINE [DAPTACEL].  The patient's past medical history, medical treatment(s), vaccination(s) and family history were not provided.  Concomitant medications included PNEUMOCOCCAL VACCINE CONJ 13V (CRM197) (PREVNAR 13) ; and INFLUENZA VACCINE INACT SPLIT 4V (FLUZONE QUADRIVALENT) all for COVID-19 vaccination.  On 05-Jan-2022, the patient received a dose of suspect DIPHTHERIA-15/TETANUS/5 AC PERTUSSIS VACCINE (strength, and formulation: unknown) at the dose of 0.5 ml (once) (batch number: C5816AA, expiry date: 26-Feb-2023) via intramuscular route in the right thigh for prophylactic vaccination. On 05-Jan-2022, the patient received a dose of suspect DIPHTHERIA/TETANUS/5 HYBRID AC PERTUSSIS/IPV(MRC5)/HIB(PRP/T) VACCINE (strength, formulation and dose: unknown) via route intramuscular (batch number: UJ572AAA, expiry date: 11-Sep-2022) via intramuscular route in the left thigh for prophylactic vaccination.  On 05-JAN-2022 the patient developed a non-serious event "administered a dose of Pentacel to a patient intramuscularly  in the left thigh, also administered (in error) a dose of Daptacel to the same patient at the same time intramuscularly in the right thigh with no reported adverse event" (product administration error) (latency: same day) following the administration of DIPHTHERIA-15/TETANUS/5 AC PERTUSSIS VACCINE and following the administration of DIPHTHERIA/TETANUS/5 HYBRID AC PERTUSSIS/IPV(MRC5)/HIB(PRP/T) VACCINE. It was reported "on 05-Jan-2022, around 10:00 am, a nurse administered a dose of Pentacel to a patient IM in the left thigh. The nurse also administered (in error) a dose of Daptacel to the same patient at the same time IM in the right thigh. The nurse reported the incident immediately to her office supervisors. There has so far been no adverse effect reported by the patient or the patient's family, but they have not yet been made aware of the administration error."  Action taken with DIPHTHERIA, TETANUS AND ACELLULAR PERTUSSIS VACCINE (DAPTACEL) and DIPHTHERIA, TETANUS, AC PERTUSSIS, IPV AND HIB VACCINE (PENTACEL) was not applicable.  At time of reporting, the outcome was Unknown for the event administered a dose of pentacel to a patient intramuscularly in the left thigh, also administered (in error) a dose of daptacel to the same patient at the same time intramuscularly in the right thigh with no reported adverse event.  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.