Hepatitis B

Hepatitis B is a viral infection caused by the hepatitis B virus (HBV) — a small, partially double-stranded DNA virus that specifically targets the liver. Once inside the body, it enters liver cells (hepatocytes), uses the cell's own machinery to replicate, and can establish a persistent infection that the immune system struggles to fully eliminate.

The infection takes two fundamentally different forms depending on how the immune system responds.

Acute hepatitis B is the initial infection. In adults who contract the virus, the immune system clears it successfully in approximately 90 to 95 percent of cases within six months, after which the person develops lifelong immunity. The acute phase may be symptomatic or completely silent.

Chronic hepatitis B develops when the immune system fails to clear the virus within six months. The risk of chronicity is strongly age-dependent — infants infected at birth have a 90 percent chance of developing chronic infection, children infected under five have a 25 to 50 percent risk, while adults who contract the virus acutely have only a 5 to 10 percent risk of going chronic. This is why hepatitis B vaccination of newborns is so critically important.

Chronic hepatitis B is not a static condition. It moves through distinct phases — immune tolerant, immune active, inactive carrier, and reactivation — each characterised by different levels of viral replication, liver inflammation, and risk of progression. Understanding which phase a patient is in guides decisions about when and how to initiate treatment.

Hepatitis B has earned its reputation as a silent disease for good reason — most people with chronic infection experience no symptoms at all, sometimes for decades.

Acute infection, when symptomatic, typically presents two to three months after exposure. Symptoms resemble a flu-like illness — fatigue, fever, muscle aches, nausea, vomiting, and loss of appetite. Some patients develop jaundice — yellowing of the skin and eyes — along with dark urine and pale stools, which indicates the liver is being affected. The symptomatic acute phase usually resolves within a few weeks.

A small proportion of patients — less than one percent — develop fulminant hepatitis B, a rare but potentially fatal form of acute liver failure where the immune response to the virus destroys so much liver tissue so rapidly that the organ fails. This is a medical emergency requiring intensive care and often urgent liver transplantation.

Chronic infection is almost always asymptomatic in its early phases. Patients feel well, their blood tests may be mildly or intermittently abnormal, and there is nothing to alert them that progressive liver damage is occurring. This is what makes chronic hepatitis B so dangerous and why screening is so important.

As chronic infection progresses toward cirrhosis, symptoms begin to emerge — persistent fatigue, abdominal discomfort in the right upper quadrant, loss of appetite, and gradually worsening jaundice. By the time these symptoms appear, significant structural liver damage has often already occurred, which underscores why the treatment of hepatitis B must begin before symptoms develop in appropriate candidates.

Hepatitis B is caused by the hepatitis B virus — a highly infectious pathogen that is transmitted through contact with infected blood, certain body fluids, and from mother to child during childbirth.

Perinatal transmission — from an infected mother to her baby during delivery — is the dominant route of transmission globally, particularly in high-prevalence regions of Asia and Africa. Babies infected at birth face a 90 percent chance of developing chronic infection, making prevention of mother-to-child transmission one of the highest-priority goals in hepatitis B control.

Sexual transmission occurs through unprotected sexual contact with an infected partner. Hepatitis B is significantly more infectious than HIV — the virus is present in semen, vaginal secretions, and blood, and can be transmitted through vaginal, anal, or oral sex.

Blood-to-blood transmission occurs through sharing of needles or syringes among people who inject drugs, needlestick injuries in healthcare workers, use of unsterilised medical or dental equipment, tattooing or body piercing with contaminated instruments, and transfusion of unscreened blood products in countries with inadequate blood safety systems.

Household transmission can occur through sharing of razors, toothbrushes, or other items that may carry traces of infected blood. Hepatitis B is not transmitted through casual contact — hugging, sharing food or water, coughing, or sneezing.

The hepatitis B virus is remarkably resilient outside the body — it can survive on surfaces for up to seven days at room temperature and remain infectious. This durability contributes to its transmissibility in healthcare and household settings.

Certain individuals and populations carry a significantly elevated risk of hepatitis B infection, and awareness of these risk factors is the first step toward targeted screening, vaccination, and where appropriate early treatment of hepatitis B.

People born in regions of high endemicity including much of sub-Saharan Africa, East and Southeast Asia, and parts of Eastern Europe face a substantially higher baseline risk, largely due to perinatal and early childhood transmission patterns.

Infants born to mothers with hepatitis B infection are at very high risk if post-exposure prophylaxis is not administered promptly at birth.

People who inject drugs are at high risk due to needle sharing. This risk extends to anyone who has ever injected drugs, even once, years in the past.

Healthcare workers and others with occupational exposure to blood and body fluids face needle-stick and splash risks. Universal precautions and vaccination are the cornerstones of occupational protection.

Men who have sex with men have an elevated risk due to sexual transmission patterns.

People with multiple sexual partners or a history of sexually transmitted infections have an increased risk of exposure.

Household contacts and sexual partners of people with known hepatitis B infection are at ongoing risk if not vaccinated.

People with HIV infection are at particular risk the two viruses share transmission routes, and HIV impairs the immune response to hepatitis B, worsening outcomes.

Patients receiving haemodialysis face an elevated risk due to repeated vascular access procedures.

The complications of chronic hepatitis B are serious, potentially life-threatening, and develop over a timeline of years to decades — which is precisely why early diagnosis and appropriate management are so important.

Cirrhosis develops in approximately 15 to 40 percent of people with untreated chronic hepatitis B over their lifetime. The chronic inflammation driven by the virus gradually replaces healthy liver tissue with scar tissue, distorting the liver's architecture and progressively impairing its function. Once cirrhosis is established, the risk of further complications rises substantially.

Hepatocellular carcinoma (HCC) — liver cancer — is one of the most feared complications of chronic hepatitis B. HBV is the leading cause of liver cancer globally, responsible for approximately 50 to 55 percent of all cases worldwide. Critically, HBV can cause liver cancer even in the absence of cirrhosis — a feature that distinguishes it from most other causes of liver cancer and that necessitates lifelong cancer surveillance in all patients with chronic HBV infection, regardless of liver fibrosis stage.

Liver failure — both acute on chronic liver failure, triggered by episodes of hepatitis flare or superinfection, and end-stage decompensated liver failure from advanced cirrhosis — can develop and may require liver transplantation.

Extrahepatic manifestations of chronic hepatitis B include a range of immune-complex mediated conditions — polyarteritis nodosa (a vasculitis affecting medium-sized blood vessels), membranous glomerulonephritis (kidney inflammation), and aplastic anaemia in rare cases. These arise when hepatitis B antigens combine with antibodies to form immune complexes that deposit in blood vessel walls and kidney tissue.

Reactivation of previously inactive hepatitis B can occur spontaneously or be triggered by immunosuppressive therapies — chemotherapy, biological agents such as rituximab, corticosteroids — and can cause severe, sometimes fatal hepatitis flares in patients who were previously clinically stable.

Diagnosing hepatitis B requires blood tests that identify the virus, assess immune response, and evaluate liver health. No single test provides the complete picture — a panel of tests is needed.

Hepatitis B surface antigen (HBsAg) is the primary marker of infection. Its presence indicates that the person is currently infected with hepatitis B — either acutely or chronically. Persistence beyond six months confirms chronic infection.

Hepatitis B surface antibody (anti-HBs) indicates immunity — either from past infection that has resolved or from successful vaccination. Its presence alongside a negative HBsAg is reassuring.

Hepatitis B core antibody (anti-HBc) — split into IgM (acute infection marker) and IgG (past or chronic infection marker) — helps distinguish acute from chronic disease and identifies people with past exposure.

Hepatitis B e antigen (HBeAg) and e antibody (anti-HBe) reflect viral replication activity. HBeAg positivity generally indicates high-level viral replication and higher infectivity. HBeAg seroconversion — losing HBeAg and developing anti-HBe — is an important treatment milestone.

HBV DNA (viral load) measures the actual amount of virus in the blood. It is the most direct measure of viral replication, guides treatment decisions, and monitors treatment response. Levels are expressed in international units per millilitre (IU/mL).

Liver function tests including ALT, AST, bilirubin, albumin, and INR assess the degree of liver inflammation and synthetic function.

Liver fibrosis assessment — via FibroScan (transient elastography), serum fibrosis markers, or liver biopsy — determines how much scarring is present and whether treatment is urgently indicated.

Hepatitis D co-infection should be tested for in all newly diagnosed HBV patients, as hepatitis D virus can only infect people who already have hepatitis B, and co-infection significantly worsens outcomes.

The treatment options for hepatitis B have expanded substantially over the past two decades, and the goals of treatment are clear: suppress viral replication, prevent liver inflammation, halt fibrosis progression, reduce the risk of cirrhosis and liver cancer, and where possible achieve functional cure.

Not every person with chronic hepatitis B requires immediate antiviral therapy. Treatment decisions are based on a combination of factors — viral load, ALT levels, degree of liver fibrosis, HBeAg status, age, and the phase of infection. Patients in the immune-tolerant phase with high viral loads but normal liver enzymes and no fibrosis may be monitored rather than treated immediately, though this approach is being increasingly reconsidered as evidence accumulates.

Nucleoside and nucleotide analogues (NAs) are the backbone of modern Hepatitis B treatment. These oral medications work by blocking the reverse transcriptase enzyme the virus uses to replicate its DNA.

Tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF) are the preferred first-line agents in most international guidelines. Both have a very high barrier to resistance — meaning the virus is highly unlikely to develop mutations that allow it to escape the drug's effects — and both achieve viral suppression to undetectable levels in the vast majority of patients. TAF is preferred in patients with kidney disease or bone density concerns as it achieves comparable antiviral efficacy at a lower systemic dose.

Entecavir is an alternative first-line agent with an excellent resistance profile and a long track record of safety and efficacy. It is widely used in patients who cannot tolerate tenofovir formulations.

These medications are generally well tolerated, taken as a single daily tablet, and can be used safely long-term. The limitation is that they suppress rather than eliminate the virus — most patients require indefinite treatment, as stopping therapy risks viral rebound and hepatitis flare.

Pegylated interferon alpha (Peg-IFN) is an injectable treatment given for a defined duration — typically 48 weeks. It works by boosting the immune system's response to the virus rather than directly suppressing viral replication. Its advantages are a finite treatment duration and a higher chance of HBsAg loss — considered functional cure — compared to nucleoside analogues. Its disadvantages are significant side effects (flu-like symptoms, fatigue, mood disturbance, bone marrow suppression) and its unsuitability for patients with cirrhosis, autoimmune conditions, or severe psychiatric history. Response rates vary considerably based on viral genotype and baseline characteristics.

The holy grail of Treatment of Hepatitis B and the focus of intense ongoing research — is a functional cure: loss of HBsAg, the surface antigen that marks active infection. Several novel therapeutic approaches are in advanced clinical trials, including RNA interference (RNAi) therapies, capsid assembly modulators, and therapeutic vaccines. While none has yet reached routine clinical practice, the field is moving faster than at any previous point, and a functional cure within the coming decade is considered a realistic goal by leading hepatologists.

Liver transplantation remains the treatment of last resort for patients who develop end-stage liver disease or liver cancer meeting transplant criteria as a result of hepatitis B. Post-transplant recurrence of HBV is prevented with a combination of hepatitis B immunoglobulin and antiviral therapy, and outcomes for HBV-related transplants are among the best of any transplant indication.

You should seek medical evaluation for hepatitis B in any of the following situations — and sooner rather than later, given the silent nature of the disease.

You have never been tested and have one or more risk factors — being born in a high-prevalence country, having a parent with hepatitis B, a history of injecting drug use, unprotected sexual contact with multiple partners, or a previous blood transfusion in a country with limited blood screening.

You have been told by a doctor or blood bank that your hepatitis B tests were abnormal or reactive and have not yet followed up with a specialist.

You are pregnant or planning to become pregnant — screening is essential because perinatal transmission is preventable with immediate intervention at birth.

You are about to start immunosuppressive therapy for any condition — chemotherapy, biological drugs, long-term steroids — as these can reactivate previously inactive hepatitis B with potentially serious consequences.

You have a household member or sexual partner who has been diagnosed with hepatitis B.

You are experiencing symptoms that could suggest liver disease — persistent fatigue, right upper abdominal discomfort, jaundice, or unexplained weight loss.

Urgent medical attention is needed if you develop sudden severe jaundice, abdominal swelling, confusion, or vomiting blood — these may indicate acute liver failure or decompensated cirrhosis requiring immediate hospital assessment.

Prevention of hepatitis B is one of medicine's genuine success stories — the tools available are highly effective, widely accessible, and capable of ending new infections if applied consistently.

Vaccination is the cornerstone of prevention. The hepatitis B vaccine is safe, highly effective — producing protective immunity in over 95 percent of healthy recipients — and provides lifelong protection in most people. The standard schedule for adults is three doses given at zero, one, and six months. In most countries, hepatitis B vaccination is now part of the routine childhood immunisation schedule, and universal infant vaccination has already produced dramatic reductions in chronic HBV prevalence in countries that have implemented it.

Birth dose vaccination is critically important. Administering the first dose of hepatitis B vaccine within 24 hours of birth — along with hepatitis B immunoglobulin in infants born to infected mothers — is over 90 percent effective at preventing perinatal transmission. This birth dose is the single most impactful intervention in preventing lifelong chronic infection.

Screening of pregnant women for HBsAg allows identification of infected mothers before delivery so that appropriate post-exposure prophylaxis can be arranged for the newborn. In mothers with very high viral loads, antiviral treatment during the third trimester further reduces transmission risk.

Safe injection practices — using sterile needles and syringes, never sharing injecting equipment — prevent blood-to-blood transmission among people who inject drugs.

Universal precautions in healthcare settings protect workers from needlestick and splash exposure.

Safe sex practices — consistent condom use and reducing the number of sexual partners — reduce sexual transmission risk.

Screening of blood donations for HBsAg and HBV DNA ensures the safety of blood transfusions in countries with robust blood banking systems.

Post-exposure prophylaxis — a combination of hepatitis B vaccine and hepatitis B immunoglobulin administered within 24 hours of a high-risk exposure — is highly effective at preventing infection after needlestick injuries, sexual assault, or other significant exposures.

Modern Treatment Options for Hepatitis B deliver genuinely encouraging results. With first-line antiviral therapy — tenofovir or entecavir — over 90 percent of patients achieve undetectable viral levels within 12 months, leading to reduced liver inflammation, fibrosis regression, and in some cases partial reversal of early cirrhosis. Long-term treatment cuts the risk of developing cirrhosis by 70 to 80 percent and substantially reduces liver cancer risk, though lifelong surveillance remains necessary.

The most important determinant of outcome is timing. Patients who receive Hepatitis B treatment before cirrhosis develops have the best prognosis and the most to gain from antiviral therapy. Every year of uncontrolled viral replication represents damage that cannot be fully reversed. Finding hepatitis B early, treating it appropriately, and monitoring it consistently is what separates a manageable chronic condition from a life-threatening one.