Hepatitis B

Cause

Hepatitis B virus (HBV), belonging to the Hepadnaviridae family.

Transmission

Infection is transmitted from person to person by contact with infected body fluids. Sexual contact is an important mode of transmission, but infection is also transmitted by transfusion of contaminated blood or blood products, or by use of contaminated needles or syringes for injections. There is also a potential risk of transmission through other skin-penetrating procedures, including acupuncture, piercing and tattooing. Perinatal transmission may occur from mother to baby. There is no insect vector or animal reservoir.

Nature of the disease

Most acute HBV infections are asymptomatic or cause mild symptoms, which are often unrecognized. Symptomatic acute disease occurs in about 1% of perinatally infected individuals, in 10% of children infected between 1 and 5 years of age, and in about 30% of individuals infected after the age of 5 years. Clinical acute hepatitis B has a gradual onset, with anorexia, abdominal discomfort, nausea, vomiting, arthralgia and rash, followed by the development of jaundice in some cases. In adults, about 1% of cases are fatal. Chronic HBV infection develops in <5% of HBV-infected adults, but more often in young children and in the majority of those infected perinatally. In some cases of chronic HBV infection, cirrhosis and/or liver cancer develop later.

Geographical distribution

The endemicity of HBV in a population is described by the prevalence of HBsAg, an HBV-specific component found in the blood (and other body fluids) in both acute and chronic stages of the infection. HBV is found worldwide, but with differing levels of endemicity. The majority of the world’s population live in countries where the prevalence of HBsAg of in the general population is high (≥8%) or intermediate (2-7%). In certain areas of North America, northern and western Europe, the southern cone of South America, Australia and New Zealand, prevalence of chronic HBV infection is relatively low (<2% ) (see map).

Risk for travellers

The risk depends on (1) the prevalence of HBV infection in the country or area of destination, (2) the extent of direct contact with blood or body fluids or of sexual contact with potentially infected individuals, and (3) the duration and type of travel. Principal risky activities include unprotected sexual intercourse with an infected person; health care interventions (medical, dental, laboratory or other) that entail direct exposure to human blood or body fluids; receipt of a transfusion of blood that has not been tested for HBV; and exposure to needles (e.g. acupuncture, piercing, tattooing or injecting drug use) that have not been appropriately sterilized. In addition, transmission from HBV-positive to HBV-susceptible individuals may occur through direct contact between open skin lesions following a penetrating bite or scratch.

Vaccine

Hepatitis B vaccine is produced by recombinant DNA technology, most commonly in yeast.

The complete vaccination series consists of three doses of vaccine; the first two doses are usually given 1 month apart, with the third dose 1–12 months later. The WHO-recommended schedule for hepatitis B immunization of children consists of a dose within 24 hours of birth followed by a second and third dose of hepatitis Bcontaining vaccines at intervals of at least 4 weeks.

A complete series of immunization provides protection for at least 25 years and, according to current scientific evidence, probably for life. Boosters are not recommended for routine immunization programmes.

Because of the prolonged incubation period of hepatitis B, some protection will be afforded to most travellers following the second dose given before travel. However, the final dose should always be given.

A combination vaccine that provides protection against both hepatitis A and hepatitis B should be considered for travellers who may be exposed to both organisms. This inactivated vaccine is administered as follows: day 0; 1 month; 6 months. A rapid schedule of day 0, 1 month and 2 months with an additional dose at 12 months, and a very rapid schedule of day 0, day 7 and day 21 with a booster dose at 12 months, have been proposed by the vaccine manufacturer and approved by national regulatory authorities in some countries.