Patient then developed seizure disorder on 4/24/2021 after receiving his 2nd RECOMBIVAX HB/Caller reports the child has since been diagnosed with "CDKL5" which his HCP states is the reason for his seizures; his first RECOMBIVAX HB vaccination on 25-FEB-2021/ his 2nd RECOMBIVAX HB vaccine on 01-APR-2021; Circumcision on 3/11/2021; Caller reported her son developed gastrointestinal issues such as gas and constipation, constant crying and irritability immediately after receiving his first RECOMBIVAX HB vaccination; Caller reported her son developed gastrointestinal issues such as gas and constipation, constant crying and irritability immediately after receiving his first RECOMBIVAX HB vaccination; Caller reported her son developed gastrointestinal issues such as gas and constipation, constant crying and irritability immediately after receiving his first RECOMBIVAX HB vaccination; Caller reported her son developed gastrointestinal issues such as gas and constipation, constant crying and irritability immediately after receiving his first RECOMBIVAX HB vaccination; This spontaneous report was received from a consumer (patient's mother) and refers to an 18-day-old male patient. The concomitant medication was reported as none. There was not known drug allergies (NKDA). The patient's concurrent conditions and medical history were not reported.  On 25-FEB-2021, the patient was vaccinated with his first (RECOMBIVAX HB) at a dose of 0.5 milliliter (ml) administered intramuscularly (vaccination scheme frequency and anatomical site of application were not reported; lot number S002770 that was verified to be valid for syringe formulation with an expiration date reported and established as 04-NOV-2021) as routine vaccination (prophylaxis).  On an unspecified date in 2021 (reported as immediately after his first vaccination), he developed gastrointestinal issues such as gas (flatulence) and constipation, constant crying, and irritability.  On 11-MAR-2021, the patient was circumcised (circumcision).  On 01-APR-2021, the patient received his second (2nd) (RECOMBIVAX HB) at a dose of 0.5 milliliter (ml) administered intramuscularly (vaccination scheme frequency and anatomical site of application were not reported; lot number S002769 that was verified to be valid for syringe formulation with an expiration date reported and established as 04-NOV-2021) as routine vaccination (prophylaxis) (inappropriate schedule of product administration).   On 24-APR-2021, the patient developed seizure disorder and was hospitalized since that date until 27-APR-2021. The patient was treated with antivirals, antibiotics (unspecified) (KEPPRA) and phenobarbital (reported as "phenobarbital").   Due to this the patient did not receive a third (3rd) dose of (RECOMBIVAX HB) (withdrawn) as parents decided to stop vaccinating him. On 18-MAY-2021, the patient received the following vaccines: (ROTETEQ) (lot number U007860 that was verified to be a valid lot number with an expiration date reported and established as 14-JAN-2022, received 2ml orally), polio, Tdap, HIB vaccines (manufacturer reported as "Sanofi") and pneumococcal vaccine (manufacturer reported as "wyeth"). It was stated that no new adverse events (AE's) were reported from these vaccines.  On an unspecified date in June 2021, the patient received a genetic testing and was stated that he had since been diagnosed with CDKL5 (CDKL5 deficiency disorder) which his health care professional stated was the reason for his seizures. Additionally, on unknown dates, the patient received a spinal tab, magnetic resonance imaging (MRI), computed tomography (CT) and blood work but details of results were not reported.  The outcome of the CDKL5 deficiency disorder was reported as not recovered. The outcome of flatulence constipation, constant crying, irritability, and circumcision was unknown.  The causality assessment between the events and (RECOMBIVAX HB) was not reported.  The reporter considered the event CDKL5 deficiency disorder (with seizures) to be medically significant and life threatening since it caused disability.  This is one of the two reports received from the same reporter (also the patient's twin brother). Sender's Comments: US-009507513-2203USA004864: