Hepatitis B Vaccines

Abstract

Hepatitis B virus, previously called the Dane particle, is a 42-nm DNA virus that belongs to the Hepadnaviridae family. HBV is primarily hepatotropic and the liver damage is produced by the cellular immune response to viral proteins in infected hepatocytes. Infection with HBV causes a broad spectrum of liver disease, including subclinical infection, acute, clinically overt self-limited hepatitis, and fulminant hepatitis. The clinical manifestations of acute hepatitis B are indistinguishable from other causes of viral hepatitis; a definitive diagnosis requires serological testing. The average incubation period is 90 days (range, 60–150 days) from exposure to onset of jaundice, and 60 days (range, 40–90 days) from exposure to onset of abnormal alanine aminotransferase (ALT) levels. Persons infected with HBV can also develop persistent infection, which can lead to chronic liver disease and death from cirrhosis or hepatocellular carcinoma (HCC). The age at acquisition of HBV infection is the main determining factor in the clinical expression of acute disease and the development of chronic infection (◘ Fig. 13.1). Fewer than 10% of children younger than 5 years who become infected have initial clinical signs or symptoms of disease (i.e., acute hepatitis B), compared with 30–50% of older children and adults. The risk for developing chronic HBV infection varies inversely with age: approximately 90% of infants infected during the 1st year of life develop chronic infection, compared with 30% of children infected between the ages 1 and 4 years and less than 5% of persons infected as adults.