The major humoral antibody response of recipients of hepatitis B vaccine is to the common a epitope, with consequent protection against all subtypes of the virus. First-generation inactivated vaccines were prepared from 22 nm HBsAg particles purified from plasma donations from chronic carriers. These preparations are safe and immunogenic but have been superseded in some countries by recombinant vaccines produced by the expression of HBsAg in yeast cells. The expression plasmid contains only the 3' portion of the HBV surface ORF and only the major surface protein, without pre-S epitopes, is produced. Vaccines containing pre-S2 and pre-S1 as well as the major surface proteins expressed by recombinant DNA technology are undergoing clinical trial.
In many areas of the world with a high prevalence of HBsAg carriage, such as China and Southeast Asia, the predominant route of transmission is perinatal. Although HBV does not usually cross the placenta, the infants of viraemic mothers have a very high risk of infection at the time of birth, and immunisation protects the infant against perinatal infection.
Immunisation against hepatitis B is now recognised as a high priority in preventive medicine in all countries and strategies for immunisation are being revised. Universal vaccination of infants and adolescents is under examination as the strategy to control the transmission of this infection. More than 90 countries now offer hepatitis B vaccine to all children, including the USA, Canada, Italy, France and most western European countries. However, immunisation against hepatitis B is at present recommended in a number of countries with a low prevalence of hepatitis B only to groups that are at an increased risk of acquiring this infection. These groups include individuals requiring repeated transfusions of blood or blood products, prolonged inpatient treatment, patients who require frequent tissue penetration or need repeated circulatory access, patients with natural or acquired immune deficiency and patients with malignant diseases. Viral hepatitis is an occupational hazard among health care personnel and the staff of institutions for the mentally handicapped, and in some semiclosed institutions. High rates of infection with hepatitis B occur in narcotic drug addicts and intravenous drug abusers, sexually active male homosexuals and prostitutes. Individuals working in areas of high endemicity are also at an increased risk of infections. Women in areas of the world where the carrier state in the group is high are another segment of the population requiring immunisation, in view of the increased risk of transmission of the infection to their offspring. Young infants, children and susceptible persons living in certain tropical and subtropical areas where present socioeconomic conditions are poor and the prevalence of hepatitis B is high should also be immunised.
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