Why does the age at which hepatitis B is acquired matter?

Hepatitis B acquired in infancy is much more likely to become a lifelong chronic infection, whereas infection acquired in adulthood is more often cleared. This is one reason vaccination programmes emphasise protecting newborns and infants.

How can a vaccine prevent a cancer?

Chronic hepatitis B infection is a major cause of hepatocellular carcinoma. By preventing the infection, hepatitis B vaccination removes that cause, and population studies have documented falling childhood liver-cancer rates after universal infant vaccination.

Hepatitis B

Hepatitis B is a liver infection caused by the hepatitis B virus (HBV), which can produce acute illness and, especially when acquired early in life, chronic infection that may progress to cirrhosis and liver cancer. Because vaccination prevents infection and its long-term sequelae, hepatitis B is an important vaccine-preventable disease (Trepo et al., 2014).

Definition

Hepatitis B is an infection by the hepatitis B virus that causes inflammation of the liver, ranging from self-limited acute hepatitis to chronic infection with risk of cirrhosis and hepatocellular carcinoma, transmitted through blood, perinatally, and sexually, and preventable by vaccination.

Scope

This topic covers hepatitis B as a clinical and public-health entity: the virus and its routes of transmission, the difference between acute and chronic infection, the link to cirrhosis and hepatocellular carcinoma, and the population-level effect of vaccination on liver cancer. It is a reference overview and does not provide treatment or prescribing guidance.

Core questions

How is hepatitis B transmitted, and why does age at infection matter?
What distinguishes acute from chronic hepatitis B?
How does chronic HBV infection lead to cirrhosis and liver cancer?
What has hepatitis B vaccination done to the incidence of liver cancer?

Key concepts

Hepatitis B virus (HBV)
Bloodborne, perinatal, and sexual transmission
Acute versus chronic infection
Age at infection and chronicity risk
Cirrhosis
Hepatocellular carcinoma
Hepatitis B vaccine

Mechanisms

HBV is transmitted through blood, perinatally from mother to infant, and sexually, and it infects hepatocytes where the host immune response largely determines the outcome. Infection acquired in infancy frequently becomes chronic, whereas infection in adulthood is more often cleared; chronic infection drives ongoing liver inflammation that can progress over years to cirrhosis and is a major cause of hepatocellular carcinoma (Trepo et al., 2014). Vaccination induces protective antibody and, by preventing infection, prevents these long-term consequences, an effect demonstrated by declining childhood liver-cancer rates after universal infant vaccination (Chang et al., 2000).

Clinical relevance

Hepatitis B illustrates how the age at which an infection is acquired shapes its long-term course, and how a vaccine that prevents infection can also prevent a cancer. This entry is descriptive and educational; it characterises the disease and the evidence on prevention and is not a basis for diagnosis or treatment in an individual patient.

Epidemiology

Chronic hepatitis B affects many millions of people worldwide and is a leading cause of cirrhosis and hepatocellular carcinoma (Trepo et al., 2014). Universal infant immunization has reduced the prevalence of chronic infection in vaccinated cohorts and lowered the incidence of childhood liver cancer, providing direct evidence that the vaccine prevents a major cancer (Chang et al., 2000).

History

The hepatitis B surface antigen was discovered in the 1960s by Baruch Blumberg and colleagues, opening the way to diagnosis and to the first hepatitis B vaccines. Programmes of universal infant vaccination followed, and long-term follow-up of vaccinated cohorts subsequently showed reductions in chronic infection and in hepatocellular carcinoma (Chang et al., 2000; Trepo et al., 2014).

Debates

How is hepatitis B's contribution to liver cancer best reduced at the population level?: Vaccination prevents new infections and has lowered childhood liver-cancer rates, but a large reservoir of existing chronic infection remains; the balance between prevention through vaccination and management of established infection shapes elimination strategy.

Key figures

Baruch Blumberg
Mei-Hwei Chang
Anna Lok

Seminal works

trepo-2014
chang-2000

Frequently asked questions

Why does the age at which hepatitis B is acquired matter?: Hepatitis B acquired in infancy is much more likely to become a lifelong chronic infection, whereas infection acquired in adulthood is more often cleared. This is one reason vaccination programmes emphasise protecting newborns and infants.
How can a vaccine prevent a cancer?: Chronic hepatitis B infection is a major cause of hepatocellular carcinoma. By preventing the infection, hepatitis B vaccination removes that cause, and population studies have documented falling childhood liver-cancer rates after universal infant vaccination.