Hepatitis B is one of the most important vaccine-preventable infectious diseases worldwide. Unlike hepatitis A, hepatitis B has the potential to become a lifelong infection, leading to serious liver complications such as cirrhosis and liver cancer. Fortunately, highly effective vaccines and post-exposure treatments have dramatically reduced the burden of disease.

Understanding how hepatitis B spreads, who is at risk, and when vaccination is recommended is essential for preventing infection and protecting long-term liver health.

What Is Hepatitis B?

Hepatitis B is caused by the Hepatitis B virus (HBV), a small double-stranded DNA virus that infects liver cells.

The virus contains two important antigens that are commonly discussed in medical practice:

• Hepatitis B core antigen (HBcAg), located within the viral core
• Hepatitis B surface antigen (HBsAg), found on the outer surface of the virus and commonly used in screening tests

These markers play an important role in diagnosing infection and determining immunity.

How Hepatitis B Spreads

Unlike hepatitis A, hepatitis B is not spread through the fecal-oral route. Instead, it is transmitted through exposure to infected blood and body fluids.

Transmission may occur through:

• Sexual contact
• Exposure to contaminated blood
• Shared needles or injection equipment
• Percutaneous injuries such as needlesticks
• Contact with infected semen, vaginal secretions, or saliva through mucosal exposure

Following exposure, hepatitis B has a relatively long incubation period.

• Average incubation: Approximately 90 days
• Typical range: 60 to 150 days

This means individuals may carry and transmit the virus long before symptoms develop.

Acute and Chronic Infection

Most healthy adults recover completely after an acute hepatitis B infection. However, approximately 5% to 10% of infected adults develop chronic hepatitis B.

People with chronic infection often have no symptoms but can continue to transmit the virus to others.

Over time, chronic hepatitis B may lead to serious complications, including:

• Liver cirrhosis
• Chronic liver failure
• Primary hepatocellular carcinoma (liver cancer)

Acute hepatitis B can also cause severe liver failure, particularly in individuals who already have chronic liver disease or fatty liver disease.

Who Is Most at Risk?

Several groups have a higher likelihood of acquiring hepatitis B because of increased exposure to blood or body fluids.

High-risk populations include:

• Sexual partners of individuals with hepatitis B
• People with multiple or new sexual partners
• Men who have sex with men (MSM)
• People who inject drugs
• Household contacts of individuals with chronic hepatitis B
• Patients receiving hemodialysis
• Healthcare workers and public safety personnel with occupational blood exposure
• Residents and staff of facilities for individuals with developmental disabilities
• Travelers and adoptees from countries where hepatitis B is common
• Adults born before 1991, before routine childhood vaccination became widespread
• Individuals with type 1 or type 2 diabetes, particularly those using shared blood glucose monitoring equipment in healthcare facilities
• Individuals living with HIV
• Patients with chronic liver disease

Vaccination is strongly recommended for these populations because of their increased risk of exposure.

Hepatitis B and Pregnancy

One of the most important routes of hepatitis B transmission is from mother to child during pregnancy and birth.

Transmission may occur:

• Across the placenta
• During delivery
• Through exposure to maternal body fluids

Without appropriate preventive treatment, approximately 40% of infants born to infected mothers develop chronic hepatitis B.

Among those children, approximately 25% will eventually die from complications such as cirrhosis or liver cancer.

Because of these serious risks, all pregnant women should be screened for hepatitis B surface antigen (HBsAg) during their first prenatal visit, regardless of previous vaccination history.

Women with ongoing risk factors may require repeat testing later in pregnancy.

Hepatitis B Vaccination

The hepatitis B vaccine is a recombinant vaccine, meaning it contains no live virus and cannot cause infection.

It is one of the most effective vaccines available.

Studies show that vaccination produces protective antibody levels in:

• 90% to 95% of healthy adults and adolescents
• Approximately 98% of healthy full-term infants

Routine vaccination has dramatically reduced hepatitis B infections worldwide.

Who Should Not Receive the Vaccine?

The primary contraindication to hepatitis B vaccination is a history of severe allergic reaction (anaphylaxis) to baker’s yeast, which is used during vaccine production.

Other vaccine allergies are associated with different immunizations, including:

• Neomycin: Contraindication for IPV, MMR, and varicella vaccines
• Gelatin: Contraindication for MMR and varicella vaccines
• Streptomycin, polymyxin B, and neomycin: Contraindication for IPV and vaccinia (smallpox) vaccines

Patients with suspected vaccine allergies should discuss vaccination options with their healthcare provider.

Is Antibody Testing Needed After Vaccination?

For most people, routine antibody testing after hepatitis B vaccination is not necessary.

However, post-vaccination testing for protective antibodies (anti-HBs) is recommended for individuals whose protection is especially important.

These groups include:

• Healthcare workers at risk of blood exposure
• Infants born to hepatitis B-positive mothers
• Sexual partners of individuals with chronic hepatitis B
• People receiving dialysis
• Individuals living with HIV
• Immunocompromised patients

Protective immunity is generally defined as an anti-HBs level of at least 10 mIU/mL.

Booster Doses

Most healthy individuals do not require routine booster doses after completing the hepatitis B vaccine series.

However, boosters may be recommended for certain high-risk populations if antibody levels fall below protective levels.

For example:

• Patients receiving hemodialysis should undergo annual anti-HBs testing.
• A booster dose is recommended if antibody levels decrease below 10 mIU/mL.

What Happens After Exposure?

Prompt treatment after exposure can significantly reduce the risk of developing hepatitis B.

Unvaccinated Individuals

People who have never been vaccinated should receive:

• Hepatitis B immune globulin (HBIG)
• The first dose of the hepatitis B vaccine series

Treatment should begin as soon as possible, preferably within 24 hours of exposure.

Fully Vaccinated Individuals

Individuals who completed vaccination but never had antibody testing may receive a single hepatitis B vaccine booster dose after exposure to a known hepatitis B-positive source.

Partially Vaccinated Individuals

People who have not completed the vaccine series should:

• Receive HBIG if indicated
• Complete the remaining hepatitis B vaccine doses

Additional Evaluation

Following a significant exposure, healthcare providers may also recommend testing for other bloodborne infections, including:

• HIV
• Hepatitis A
• Hepatitis C

Occupational exposures, such as needlestick injuries, should be managed according to institutional protocols and expert recommendations.