Generalized tonic-clonic seizure; This spontaneous serious safety report with reference number 02153746 (Interaction number 02153745) was received by a partner on 25-APR-2022 and forwarded to Agency on 26-APR-2022 from a health care professional.  A 4-month-old female patient, with medical history of ventricular septal defect, had been vaccinated with a 2nd dose of Vaxelis (Batch number U7125AA, expiration date 15-JUL-2024) on 13-APR-2022 for routine vaccination.   The following concomitant vaccinations were reported: Prevnar 13 and RotaTeq administered on 13-APR-2022 for routine vaccination.  On 21-APR-2022, eight days after receiving the vaccination with Vaxelis, the patient experienced generalized compulsive seizures that lasted for 45 seconds. The patient was taken to the emergency department and kept under observation for several hours.   On an unspecified date, head ultrasound and labs were performed, and results were normal.  It was reported that the patient did not experience any seizure activity since the initial seizure on 21-APR-2022.   Action taken with Vaxelis was not applicable.   At the time of this report, the outcome of the event was Recovered/Resolved.   The reporter did not provide an assessment of the causal relationship between Vaxelis and the reported event of generalized compulsive seizures.   Further information is expected.  FOLLOW-UP INFORMATION with reference number 02153746 (Interaction number 02153745) was received by MSD on 02-May-2022 and forwarded to Agency on 03-May-2022 from a health care professional.  On 22-Apr-2022, head ultrasound was normal. CMP and blood glucose were normal. On 29-Apr-2022, EEG was normal.  At the time of this report, the outcome of the event was Recovered/Resolved.   The reporter assessed the event of generalized compulsive seizures to have reasonable possibility of causal relationship to Vaxelis, providing "unknown, possible" to suggest a causal relationship.  Further information is expected.  FOLLOW-UP INFORMATION was received by Fax on 18-May-2022, from a health care professional (HCP).  The HCP reported that the patient was seen in ER, the seizure had resolved and no medicines were given to the patient. Moreover, the patient did not present any fever around the time of the event.  The reporter confirm that the seizure experienced by the patient was a "Generalized tonic-clonic seizure".  No further information is expected given that the reporter replied to all the queries.   COMPANY COMMENT:   Generalized tonic-clonic seizure is assessed as serious due to the event being medically significant.   Generalized tonic-clonic seizure is unlisted for Vaxelis as per the Reference Safety Information (CCDS).  Considering the reporter's causality (related), and despite the long onset latency for the Generalized tonic-clonic seizure (8 days after vaccination), and the existence of alternative explanations (co-suspect vaccines), the causal relationship between Vaxelis and the event Generalized tonic-clonic seizure cannot be excluded and is assessed as related. Given the incidence of this event among the pediatric population, a spontaneous event has been taken into consideration for this assessment.  This single individual case safety report does not modify the benefit/risk balance of this product. Therefore, no change in the label or other measures is recommended at this time. However, the company will continue to monitor all respective reports received and based on cumulative experience, will re-evaluate the available evidence on an ongoing basis.; Sender's Comments: Generalized tonic-clonic seizure is assessed as serious due to the event being medically significant.   Generalized tonic-clonic seizure is unlisted for Vaxelis as per the Reference Safety Information (CCDS).  Considering the reporter's causality (related), and despite the long onset latency for the Generalized tonic-clonic seizure (8 days after vaccination), and the existence of alternative explanations (co-suspect vaccines), the causal relationship between Vaxelis and the event Generalized tonic-clonic seizure cannot be excluded and is assessed as related. Given the incidence of this event among the pediatric population, a spontaneous event has been taken into consideration for this assessment.  This single individual case safety report does not modify the benefit/risk balance of this product. Therefore, no change in the label or other measures is recommended at this time. However, the company will continue to monitor all respective reports received and based on cumulative experience, will re-evaluate the available evidence on an ongoing basis.