This case was reported in a literature article and described the occurrence of vaccination failure in a 21-year-old female patient who received Hepatitis B vaccine. Concurrent medical conditions included intravenous drug user (ivdu), staphylococcus aureus endocarditis (secondary to methicillin-susceptible Staphylococcus aureus), non-ischemic cardiomyopathy (ejection fraction 15%) and hepatitis c (positive for hepatitis C viral antibodies with an undetectable hepatitis C viral RNA initially followed by a low level viremia). On an unknown date, the patient received Hepatitis B vaccine at an unknown dose. In November 2013, several years after receiving Hepatitis B vaccine, the patient experienced vaccination failure (serious criteria GSK medically significant) and hepatitis b (serious criteria GSK medically significant). On an unknown date, the outcome of the vaccination failure and hepatitis b were unknown. The reporter considered the vaccination failure to be related to Hepatitis B vaccine. It was unknown if the reporter considered the hepatitis b to be related to Hepatitis  B vaccine. Additional information was provided: This case was reported in a literature article and it described the occurrence of an occult hepatitis B infection in a 21-year-old female who had received unspecified hepatitis B vaccines (manufacturer unknown). The patient was an intravenous drug user. Concomitant medical conditions included tricuspid valve endocarditis secondary to methicillin-susceptible Staphylococcus aureus which was complicated by non-ischemic cardiomyopathy (ejection fraction 15%) for which the patient was hospitalized at the time of the event. No further information on the patient's concurrent medical conditions, medical and family history or concomitant medication was provided. On unspecified dates, the patient had received an unspecified number of hepatitis B vaccines for prophylaxis as part of a nursing training programme. Dosages unknown; administration routes and sites unspecified; batch numbers was not provided. In November 2013, date unspecified, several years after the vaccination, the patient tested positive for hepatitis C viral antibodies with an undetectable hepatitis C viral RNA initially followed by a low level viremia whole admitted due to an tricuspid valve endocarditis. She was persistently negative for hepatitis B surface antigen, but she tested positive for hepatitis B e antigen and hepatitis B viral DNA in 2 separate occasions. In addition to this, the patient became positive for hepatitis B core antibodies during her admission. However, she was negative for hepatitis B e antigens and hepatitis B core antibodies and had no detectable hepatitis B viral DNA six months later. According to the authors, this meant that the infection had subsided. This case was considered as medically relevant by GSK due to suspected vaccination failure. The patient was found to be positive for hepatitis C antibodies (undetectable DNA) and hepatitis B surface antibodies and negative for hepatitis B core total antibodies and human immunodeficiency virus antibodies on 19 November 2013. She tested negative for hepatitis B surface antigens on 17 January 2014 with an aspartate aminotransferase of 1873 IU/mL, an aspartate aminotransferase of 4518 IU/mL and a hepatitis C viral load of 902 IU/mL. Her hepatitis C viral load had dropped to 642 IU/mL on a test performed the following day, but she was found to have a hepatitis B viral load of 8364 IU/mL. Repeat liver enzymes level performed on 24 January 2014 showed a drop on her aspartate aminotransferase and aspartate aminotransferase levels (561 IU/mL and 203 IU/mL respectively). A serology performed on 25 January 2014 was negative for hepatitis B surface antigens, positive for hepatitis B surface and core (total) antibodies as well as for hepatitis B e antigens, but negative for hepatitis B e antibodies. She had a viral load of 174 and 4608 IU/mL for hepatitis C and hepatitis B virus respectively at the time. The results for hepatitis B surface antibodies, hepatitis B e antigens and hepatitis B e antibodies were when tested again 4 days later, but her hepatitis viral load had increased to 5243 IU/mL. On 30 January 2014, the patient tested positive for hepatitis B c total antibodies but negative for hepatitis B c immunoglobulin M antibodies. Finally, the patient's hepatitis C and hepatitis B viral load was undetectable on 9 July 2014 and she was negative for hepatitis B surface antigen, positive  for hepatitis B surface and core total antibodies and negative for hepatitis B e antigens. Nine full-length clones of her hepatitis B virus were sequenced by the authors and all were found to be genotype D3 without any know diagnostic escape mutations. Immune complexes that could have prevented hepatitis B surface antigen detection were not observed either. No antiviral treatment was provided for the viral infections, treatment for the other medical conditions was unknown. The authors referred to the occult as a vaccine breakthrough infection. The authors concluded that "a case of resolving occult hepatitis B following adult vaccination in a hepatitis C-positive intravenous drug user. Previous studies have indicated that while hepatitis B vaccination is effective at preventing chronic hepatitis B infection, it may be less effective at preventing Hepatitis B surface antigen-negative hepatitis B infection. This case highlights the importance of carefully determining the hepatitis B viral status of high-risk individuals, as vaccination history and the presence of hepatitis B surface antigens may not be adequate to rule out hepatitis B infection, even in the absence of hepatitis B surface antigen."