Single Seizure Unspecified Type; This 21-month-old male subject was enrolled in a blinded study. The subject received the 4th dose of Bexsero vs Placebo (intramuscular, right thigh) on 16-OCT-2019, for prophylaxis. The subject received the 3rd dose of DTPa-HBV-IPV (intramuscular, left thigh) on 26-APR-2019, for prophylaxis. The subject received the 3rd dose of Hiberix (intramuscular, right thigh) on 26-APR-2019, for prophylaxis. The subject received the 2nd dose of Rotarix lyophilized formulation (oral) on 04-FEB-2019, for prophylaxis. The subject received the 1st dose of M-M-R II (subcutaneous, right arm) on 16-OCT-2019, for prophylaxis. The subject received the 1st dose of Varivax (subcutaneous, left arm) on 16-OCT-2019, for prophylaxis. Co-suspect products included Prevenar 13 (Non-GSK Comparator) (Prevenar 13) for prophylaxis. On 05-JUL-2020, 263 days after receiving Bexsero vs Placebo, M-M-R II and Varivax, 436 days after receiving DTPa-HBV-IPV and Hiberix and 517 days after receiving Rotarix lyophilized formulation, the subject developed mild – grade 1 seizure (Verbatim: Single Seizure Unspecified Type). Serious criteria included clinically significant/intervention required. The outcome of seizure was resolved on 05-JUL-2020. Diagnostic results (reference ranges are provided in parenthesis if available): Blood magnesium- 05-JUL-2020 2.4 mg/dL, (1.70-2.30). Body temperature- 05-JUL-2020 98.3 (taken orally). Lymphocyte count- 05-JUL-2020 78.0 percent, (20.00-70.00). The investigator considered that there was no reasonable possibility that the seizure may have been caused by Bexsero vs Placebo, DTPa-HBV-IPV, Hiberix, Rotarix lyophilized formulation, M-M-R II and Varivax. Other possible cause(s) of the seizure included DTPa-HBV-IPV vaccine PRE-FILLED SYRINGE DEVICE and Rotavirus vaccine ORAL APPLICATOR DEVICE. The company considered that there was no reasonable possibility that the seizure may have been caused by Bexsero vs Placebo, DTPa-HBV-IPV, Hiberix, Rotarix lyophilized formulation, M-M-R II and Varivax. 05JUL2020 mother was trying to put subject down to nap, he was crawling to the edge of their bed, but did not fall, and then suddenly went limb. Mom flipped him over, eyes were fluttering, body was limp, lasted about 3 minutes. Did not stop breathing, did not turn blue, did not wet himself. Mom called EMS. The subject regained his strength and Baseline status. He has been doing well recently with no recent illness. No head trauma recently. No family history of epilepsy. Subject was discharged home in stable condition after being observed in Emergency Department for 3 hours. No medications were given. The only procedure done was lab draw for complete blood count (CBC) and Electrolytes. Labs were normal except for Magnesium 2.4 mg/dL (normal range 1.7-2.3 mg/dL) and lymphocytosis ith lymphocytes at 78 percent (normal range 20-70 percent). No other treatments were done. No family history of epilepsy. No previous history of seizures documented in medical record. Loss of consciousness reported. Event occurred more than 48hrs after last vaccination (15NOV2019), so hypotonic hyporesponsive episode excluded. No birth complications reported. No fever. The seizure was witnessed by study parents or relatives. The date of first seizure was 5/Jul/2020 and time of first seizure was unknown. No fever at the time or immediately before generalized convulsive seizure. Duration of seizure in minutes (approximately): 3 minutes. Number of generalized convulsive seizures: 1. No past history of similar events. Familial history of similar events. Type of Seizure: Single Seizure, unspecified type. Diagnostic certainty level: Level 1; Witnessed sudden loss of consciousness AND generalized, tonic, clonic, tonic-clonic, or atonic motor manifestations. No Familial history of similar events. Investigator reported SAE term as Single Seizure Unspecified Type. On 28May2021, the SAE Single Seizure Unspecified Type was marked as Other AESI by the Investigator. This case contains an event assessed by the investigator as a serious adverse event of special interest (AESI). Follow up information received on 14-Jan-2025. Summary of changes: General narrative updated. Upon internal review the case was updated on 20-Jan-2025. Route of administration was corrected for Rotarix lyophilized formulation, M-M-R II and Varivax. Anatomical location added for Bexsero vs Placebo, Prevnar 13, Hiberix, M-M-R II, Varivax, device causality updated as unknown.; Sender’s Comments: A case of Seizure, 263 days after receiving the 4th dose of Bexsero vs Placebo and Prevnar 13, 1 st dose of M-M-R II and Varivax, 436 days after receiving 3rd dose of DTPa-HBV-IPV vaccine pre-filled syringe device injection syringe, and Hiberix, 517 days after receiving 2nd dose of Rotarix vaccine oral applicator device, co-administered with PCV and routine vaccines, in a 21-month-old male subject. Report is inconsistent with causal relation to the vaccine product, considering implausible time to onset.