Hepatitis B virus

Importance: Hepatitis B virus (HBV) infection affects an estimated 254 million people worldwide and causes approximately 1.1 million deaths annually. In 2022, there were approximately 1.2 million new HBV infections worldwide and 14 000 in the US.

Observations: HBV is a DNA virus transmitted through percutaneous or mucosal exposure to infected blood, semen, or body fluids. Mother-to-child transmission, which is the principal cause of chronic HBV infection globally, occurs in 70% to 90% of infants born to mothers who are hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) positive and in 5% to 20% of those born to HBsAg-positive/HBeAg-negative mothers. However, HBV vaccination and administration of hepatitis B immune globulin within 12 to 24 hours of birth prevent approximately 94% of perinatal infections, and adding antiviral therapy in pregnant women with high HBV DNA reduces transmission to less than 1%. Although universal birth-dose HBV vaccination is the most effective strategy for eliminating HBV infection, global birth-dose HBV vaccine coverage was only 45% in 2024. The risk of developing chronic infection (HBsAg positive for more than 6 months) is 90% if HBV infection occurs during infancy, 30% in children aged 1 to 5 years, and less than or equal to 5% in immunocompetent adolescents and adults. HBV infection is diagnosed by serologic testing: HBsAg indicates ongoing infection, antibody to HBsAg indicates immunity, and antibody to hepatitis B core antigen indicates ongoing or past infection. Serum HBV DNA levels quantify virus-replication activity. Assessment of liver inflammation and fibrosis with alanine aminotransferase (ALT) and noninvasive tests such as Fibrosis-4 index and liver elastography guide treatment decisions. Chronic HBV infection may progress to cirrhosis and hepatocellular carcinoma (HCC); the 5-year cumulative risk of cirrhosis is 8% to 15% in untreated chronic HBV infection, and annual HCC incidence is 3% to 5% among patients with cirrhosis. Antiviral therapies-pegylated interferon alfa and nucleos(t)ide analogues (entecavir or tenofovir)-suppress HBV DNA replication and reduce the risk of HCC by approximately 50%. Antiviral treatment is recommended for all patients with chronic HBV and cirrhosis and for those without cirrhosis who have high HBV DNA with elevated ALT or significant inflammation/fibrosis. Patients at high risk of HCC should undergo surveillance with ultrasonography and alpha-fetoprotein testing every 6 months.

Conclusions and relevance: HBV infection causes approximately 1.1 million deaths annually worldwide. Universal HBV vaccination, particularly birth-dose administration, is the most effective strategy to prevent HBV infection. Among patients with HBV infection, antiviral therapy decreases progression to cirrhosis and liver failure and reduces the risk of HCC.