Hepatitis B

Hepatitis B virus (HBV) infection causes subclinical infection, acute hepatitis, fulminant hepatitis, and chronic hepatitis. The age of the individual at acquisition of HBV infection is the single most important factor in determining the clinical manifestation of infection as well as the development of chronic infection. Younger individuals are the least likely to have clinical illness but have the greatest likelihood of chronic hepatitis B infection.

Persons with chronic HBV infection (also called “chronic carriers”) are usually asymptomatic and often unaware that they are infected. About 5% of adults and 90% of newborns who are infected will develop chronic HBV infection. Approximately 25% of chronic HBV carriers die prematurely from chronic liver disease or hepatocellular carcinoma. Annually in the USA, 3000–4000 persons die from cirrhosis and another 1000–1500 from liver cancer due to HBV.

In the USA, HBV is transmitted most frequently by perinatal transmission from infected mothers to their newborns at birth, by sexual contact, by percutaneous exposure to body fluids (such as serum, saliva, semen, and vaginal fluid), or by nonsexual person-to-person contact.

The detection of an antigen in the blood of Australian aborigines in 1965—now known to have been a marker for hepatitis B surface antigen (HBsAg)— quickly led to initial trials of boiled serum as a potential vaccine. Initial plasma-derived vaccines, licensed in the USA in 1981, were quickly supplanted after the elucidation of the genomic sequence of HBV, including sequencing of the HBsAg. Recombinant HBsAg vaccine, manufactured in yeast, was licensed in the USA in 1986.

Initial HBV vaccine interventions in the USA between 1981 and 1991 targeted the highest risk groups of acquiring HBV infection by screening mothers for HBsAg (in order to begin immunization of their infants in the nursery and to give them hepatitis B immunoglobulin [HBIG]) and by attempting to identify those with risk factors. Unfortunately, many with risk factors (such as heterosexuals with contact with infected persons; those who have had multiple sexual partners or whose partner has had multiple sexual partners; intravenous drug users; and men who have sex with men) either did not know that they had a risk factor, were hard to reach, or denied having a risk factor.

In 1991, the vaccination recommendation was expanded to include immunization of all newborn infants for the following reasons:

• Universal immunization of children has proven to be the most effective immunization strategy
• Approximately 30% of people who get HBV infec- tion do not have any identifiable risk factors, including children
• HBV infection of children of all ages leads to an increased risk to develop chronic HBV infection
In 2005, HBV vaccine recommendations were expanded further to include the following:
• Routine infant hepatitis B vaccination to begin at birth, before hospital discharge
• Implementation of enhanced programs to detect perinatal HBV infection
• Routine immunization of all previously unvacci- nated children and adolescents
• Identification and vaccination of previously unvaccinated adults who were at increased risk for infection by virtue of being in settings where a high proportion of adults are likely to have a risk factor for HBV (such as incarcerated persons)

Many countries that have instituted routine HBV immunization of infants, children, and adolescents have begun reporting declines in HBV infections and declines in HBV-related liver disease. In the USA, a number of states have also have also begun to report similar outcomes.