Hepatitis B in depth.

Overview

Hepatitis B is a serious liver infection caused by the Hepatitis B virus (HBV), a partially double-stranded DNA virus in the family Hepadnaviridae. Approximately 296 million people worldwide live with chronic HBV infection, and the disease causes approximately 820,000 deaths annually — primarily from liver cirrhosis and hepatocellular carcinoma (liver cancer). HBV is the most common serious liver infection in the world and the leading cause of liver cancer globally. The virus is 50–100 times more infectious than HIV. A safe, highly effective vaccine has been available since 1982 — HBV is entirely preventable — yet coverage gaps mean new infections continue.

The risk of chronic infection is critically dependent on the age at which infection occurs. In perinatal transmission (mother to newborn), 90% of infected neonates develop chronic HBV. In children aged 1–5 years, chronicity risk is 25–50%. In adults, only 5% progress to chronic infection — most adults clear acute HBV naturally. This age-dependence explains why endemic HBV transmission is dominated by perinatal and early childhood routes in high-burden regions (sub-Saharan Africa, Asia), where 90% of the disease burden originates from childhood infections.

History & Origin

Baruch Blumberg discovered the "Australia antigen" (now known as HBsAg, the hepatitis B surface antigen) in 1965 — a discovery that earned him the 1976 Nobel Prize in Physiology or Medicine. The hepatitis B virus itself was identified by David Dane in 1970 (the "Dane particle"). The first plasma-derived hepatitis B vaccine was approved in 1981; the recombinant DNA vaccine followed in 1986. Both are highly effective and form the backbone of global HBV prevention.

The world has known about hepatitis B since at least the 1800s, when "serum hepatitis" was observed following smallpox vaccination campaigns that used pooled human material. During World War II, a massive yellow fever vaccine campaign inadvertently infected 330,000 US soldiers with hepatitis B through contaminated human serum used as a vaccine stabilizer.

Transmission

HBV is transmitted through contact with infectious blood or body fluids. The virus can survive outside the body for at least 7 days and remains infectious during this time.

• Perinatal transmission: Mother-to-child transmission during birth (not across the placenta). Highest risk when mother is HBeAg-positive (high viral load). Without prophylaxis, transmission rate is 70–90% from HBeAg-positive mothers.
• Sexual transmission: Unprotected sex with an infected partner. Risk per sexual contact is higher than HIV. Anal sex carries highest risk; vaginal sex also transmits.
• Percutaneous exposure: Sharing needles/syringes (intravenous drug use); needlestick injuries in healthcare workers; tattooing and piercing with unsterilized equipment.
• Horizontal transmission in childhood: Skin-to-skin contact (biting, scratching), sharing razors or toothbrushes, or contact with open wounds in households with chronic carriers — a major transmission route in high-burden countries.
• Blood transfusion / organ transplant: Risk near-zero in countries with mandatory blood screening but significant in low-income settings without universal blood testing.
• HBV is NOT transmitted by: casual contact, hugging, sharing food/water, coughing, sneezing, or insect bites.

Clinical Phases

Diagnosis

• HBsAg (Hepatitis B surface antigen): First marker to appear (4 weeks post-infection); positive = current infection (acute or chronic). Persists >6 months = chronic HBV.
• Anti-HBs (Surface antibody): Develops after infection or vaccination; indicates immunity. Positive after vaccination = protected.
• HBeAg (e antigen): Marker of active viral replication and high infectivity. Positive = high viral load, high transmission risk.
• Anti-HBe: Appears as HBeAg clears; seroconversion (HBeAg to anti-HBe) marks reduced replication — treatment goal.
• Anti-HBc (core antibody): IgM anti-HBc = acute HBV; IgG anti-HBc = past or current infection. Anti-HBc positive + HBsAg negative = resolved past infection.
• HBV DNA (viral load): Quantitative PCR; measures viral replication; guides treatment decisions and monitors response. >2,000 IU/mL often threshold for treatment initiation.
• Liver function tests: ALT/AST elevation indicates hepatic inflammation. Normal ALT does not exclude fibrosis.
• Fibroscan / liver biopsy: Assesses degree of liver fibrosis — critical for staging chronic HBV and deciding treatment timing.

Treatment

No complete cure for chronic HBV exists. Antivirals suppress viral replication and prevent disease progression but rarely eliminate HBV (functional cure = HBsAg loss, occurring in ~1% per year on treatment).

Preferred Antivirals

• Tenofovir disoproxil fumarate (TDF): First-line for most patients; very high barrier to resistance; highly effective. Monitor renal function and bone density. Tenofovir alafenamide (TAF) has better renal/bone safety profile.
• Entecavir (ETV): First-line alternative; excellent efficacy; high barrier to resistance in treatment-naive patients; renally cleared — dose adjust in renal impairment.
• Pegylated interferon-alfa (PegIFN): Finite course (48 weeks); immune-modulating; higher HBeAg seroconversion rates; significant side effects (flu-like symptoms, depression, cytopenias); not suitable for all patients. Preferred in young patients with active immune response seeking finite therapy.

Treatment Goals

• Suppress HBV DNA to undetectable levels
• Normalize ALT (prevent ongoing liver damage)
• Achieve HBeAg seroconversion (loss of HBeAg, gain of anti-HBe)
• Prevent cirrhosis and hepatocellular carcinoma
• Functional cure (HBsAg loss) — rare but possible with long-term treatment

Prevention of Vertical Transmission

• All HBsAg-positive pregnant women: screen HBV DNA; antiviral therapy (TDF) from 28 weeks if viral load >200,000 IU/mL
• Newborns of HBsAg-positive mothers: hepatitis B vaccine within 12 hours of birth PLUS hepatitis B immunoglobulin (HBIG) — reduces perinatal transmission by >95%

Prevention & Vaccine

• Hepatitis B vaccine: Recombinant vaccine; 3-dose series (0, 1, 6 months); >95% effective in preventing HBV infection and its consequences including liver cancer. First licensed in 1982. WHO recommends birth dose within 24 hours, then 2 additional doses in infant immunization schedule.
• Birth dose timing: The birth dose (within 24 hours) is critical — it prevents mother-to-child transmission in combination with HBIG. A delayed first dose misses the window for perinatal protection.
• Hepatitis B immunoglobulin (HBIG): Passive prophylaxis used post-exposure (needlestick injuries, newborns of infected mothers); must be given within 24 hours of exposure.
• Safe injection practices: Use sterile needles; never share syringes or drug paraphernalia; ensure tattooing/piercing uses sterile equipment.
• Safe sex: Consistent condom use reduces sexual transmission risk; vaccination of uninfected partners.
• Blood safety: Universal screening of blood donations for HBsAg.

Global Impact

Hepatitis B is the most common chronic bloodborne viral infection in the world. The Western Pacific and African regions carry 68% of the global burden. Countries with the highest prevalence (>8% HBsAg seroprevalence) include much of sub-Saharan Africa, China, Southeast Asia, and Pacific Island nations. An estimated 6% of the world's population is chronically infected.

HBV causes approximately 820,000 deaths annually — more than twice HIV's mortality. It is the leading cause of hepatocellular carcinoma (HCC), which kills over 700,000 people per year. Despite 95%+ vaccine efficacy and a vaccine available since 1982, birth-dose coverage globally remains inadequate, particularly in Africa where many births occur outside health facilities.

WHO's Global Health Sector Strategy on Viral Hepatitis aims to eliminate viral hepatitis as a public health threat by 2030 — defined as 90% reduction in new infections and 65% reduction in mortality compared to 2015. Achieving this requires near-universal birth-dose vaccination, widespread testing, and antiviral treatment scale-up. As of 2024, only about 12% of people living with chronic HBV are diagnosed, and only 5% are on treatment.

Frequently Asked Questions

Sources & Citations