Hepatitis B is one of the main human diseases and a serious worldwide public health problem. It has been possible to avoid it since 1982 as a result of an effective, safe vaccine. There are estimated to be 2 billion people infected with the virus, including more than 350 million who have become chroniccarriers and can transmit the virus for years.
Chronic carriers are at high risk of dying from cirrhosis or livercancer, diseases which cause approximately one million deaths a year. The hepatitis B vaccine does not cure chronic carriers, but it is 95% effective in preventing development of chronic carrier status. It is also the first vaccine to become available against one of the main human cancers.
In 1991, the World Health Organisation recommended that all children be vaccinated against hepatitis B. At present, 116 countries have added this vaccine to their routine vaccination programme. However, those who need it most, children in the poorest countries, do not get the vaccine, as it is too expensive for their government. Fortunately, the hepatitis B vaccine will soon be available in these countries with the help of the Global Alliance for Vaccines and Immunization (GAVI) and the Global Fund for Children's Vaccines.
Who is infected with the hepatitis B virus?
In most developing countries (sub-Saharan Africa, a large part of Asia and in the Pacific basin) most people who are infected with the virus were infected during childhood. Chronic carriers represent 8% to 10% of the population. In these regions, liver cancer caused by hepatitis B is one of the three leading causes of cancer deaths in humans.
High rates are also seen in the Amazon and in south of eastern and central Europe. Chronic carriers make up approximately 5% of the population in the Middle East and in the Indian sub-continent. The infection is less common in western Europe and North America, where less than 1% of the population are chronic carriers.
People who are infected in early childhood are those at most risk of becoming chronic carriers. Consequently, 90% of children infected before the age of one, and 30% to 50% of children infected between the ages of one and four years old will develop chronic infection. The risk of dying from cirrhosis and liver cancer caused by the hepatitis B virus is approximately 25% if the infection occurs during childhood.
How is the hepatitis B virus transmitted?
Hepatitis B is transmitted by contact with blood or biological fluids from an infected person in the same way as the human immunodeficiency virus (HIV) which causes AIDS. On the other hand, the hepatitis B virus is 50 to 100 times more infectious than the AIDS virus. The major routes through which the infection is transmitted are:
* Mother-to-child transmission at childbirth; * Child-to-child transmission; * High-risk injections and transfusions; * Sexual contact.
Throughout the world, the virus is most frequently transmitted from mother to child, between children in the same family and by re-using unsterilised syringes and needles. In many developing countries, almost all children are infected with the virus.
The methods of transmission are different in many industrial countries (such as western Europe and North America). Mother to child and child to child transmission accounted for more than a third of chronic infections before hepatitis B vaccination was incorporated into the child vaccination programmes. Transmission in this part of the world mainly occurs in early adulthood from sexual intercourse or the use of injectable drugs. In addition, the hepatitis B virus is the main risk of infection in healthcare staff, most of whom have themselves vaccinated.
The virus cannot be transmitted by contaminated water or food, or by simple contact in the workplace.