administered only the lyophilized hib component of pentacel and used sterile water to dilute it with no reported adverse event; Initial information received on 23-Jan-2025 regarding an unsolicited valid non-serious case received from a other health professional. This case involves an unknown age / gender patient who was administered only the lyophilized HIB component of diphtheria/tetanus/5 hybrid AC pertussis/IPV(VERO)/HIB(PRP/T) vaccine [Pentacel (VERO)] and used sterile water to dilute it with no reported adverse event. The patient’s past medical history, medical treatment(s), vaccination(s) and family history were not provided. On 10-Jan-2025, the patient received an unknown dose of lyophilized HIB component of diphtheria/tetanus/5 hybrid AC pertussis/IPV(VERO)/HIB(PRP/T) vaccine Suspension for injection (strength, expiry date and lot number not reported) via unknown route in unknown administration site and used sterile water to dilute it with no reported adverse event (single component of a two-component product administered) (latency- same day). Reportedly, they wanted to know if the HIB dose counted as a dose. They had a follow up question with what they should do about the DTaP-IPV component. Information on the batch number was requested corresponding to the one at time of event occurrence. 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.