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Hepatitis B is a liver infection caused by the hepatitis B virus (HBV), a DNA virus transmitted through sexual contact, blood, and mother-to-child transmission. While more than 90% of adult primary infections resolve spontaneously, perinatal and early childhood infections frequently lead to chronic carrier status, with the risk of progressing to chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma (HCC). This article comprehensively explains HBV transmission routes, symptoms, testing (HBsAg, HBV-DNA, HBeAg/anti-HBe), treatment (nucleoside/nucleotide analog [NA] therapy, pegylated interferon), HBV vaccine efficacy, and the risks of leaving the infection untreated.
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For those considering hepatitis B testing or vaccination | HBsAg and anti-HBs testing, 3-dose HBV vaccine series, men’s-only clinic, free initial consultation
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“I was told my HBsAg is positive.” “My partner was diagnosed as a hepatitis B carrier.” “I heard I should get vaccinated.” Triggers like these are prompting more people to look into hepatitis B.
Hepatitis B is an infectious disease caused by the hepatitis B virus (HBV), with an estimated 250 million chronic carriers worldwide, making it a major public health concern. In Japan, there are approximately 1.1 to 1.4 million carriers. While new carrier numbers have dropped sharply since 1986 thanks to maternal-to-child transmission prevention programs, adult infections through sexual contact and blood exposure continue to occur.
Hepatitis B is characterized by being “preventable by vaccine,” “sometimes resolving spontaneously,” “carrying a risk of fulminant hepatitis,” and “potentially progressing to chronic hepatitis, cirrhosis, and HCC if chronic carriage develops.” It differs from hepatitis C in transmission routes, treatment, and prevention strategies.
This article explains the fundamentals of HBV, including transmission, symptoms, testing, treatment, and prevention, as guided by physicians at our STI clinic.
Hepatitis B is a liver infection caused by the hepatitis B virus (HBV). HBV is a DNA virus belonging to the family Hepadnaviridae, and it establishes persistent infection by integrating into hepatocytes.
The natural history of HBV infection differs greatly depending on the age at which infection occurs. More than 90% of adult primary infections resolve spontaneously, while perinatal infections and those acquired before age 3 frequently progress to chronic carriage because the immune system is too immature to clear the virus.
In Japan, genotype C predominates (about 80%) and tends toward chronicity. However, adult infections with genotype A (originating from Western countries) have been increasing in recent years, and genotype A is known to have a higher chronicity rate (around 10%) after acute infection compared with Japan’s predominant genotype C.
HBV is transmitted via blood and body fluids (semen, vaginal secretions, saliva, sweat, etc.). It is approximately 100 times more infectious than HCV, and even a minute amount of body fluid can establish infection. In men, sexual contact is the most common route of transmission.
HBV can survive in the environment for approximately one week, and even dried blood retains infectivity. Awareness of prevention is important in household and close-contact settings.
The symptoms of hepatitis B vary significantly depending on the stage of infection, the age at which infection occurred, and the host’s immune status.
The incubation period averages 60-90 days (range: 30-180 days). When symptomatic, the following symptoms may appear, though subclinical (asymptomatic) infection is also common.
Approximately 1-2% of acute hepatitis B cases progress to fulminant hepatitis, with rapid hepatocyte necrosis leading to liver failure. Characterized by neuropsychiatric symptoms (coma) appearing within 8 weeks of onset, it is an extremely high-risk emergency with a mortality rate of 60-80%.
A state in which HBsAg remains positive for 6 months or longer after infection. Most cases are asymptomatic, but active hepatitis is more likely during the HBeAg-positive phase, while inflammation tends to settle after seroconversion to HBeAg-negative/anti-HBe-positive status.
Hepatitis B testing combines multiple markers to comprehensively determine infection status, carrier state, and disease activity.
A test for the HBV surface antigen, an envelope protein. A positive result means current HBV infection, indicating acute hepatitis, carrier state, or chronic hepatitis. It is the first-line screening test.
A neutralizing antibody against HBsAg. A positive result indicates immunity acquired either through recovery from past infection or vaccination. Levels of 10 mIU/mL or higher are considered protective.
An antibody against the HBV core antigen. A positive result indicates past HBV infection and remains positive in both current carriers and those who have cleared the virus spontaneously. Because vaccination does not produce anti-HBc, this marker is critical for distinguishing prior infection from vaccine-induced immunity.
HBeAg is a marker of active viral replication. HBeAg positivity indicates a high viral load and high infectivity, while anti-HBe positivity with HBeAg negativity (after seroconversion) indicates lower viral load and reduced infectivity.
Quantification of HBV-DNA in blood by real-time PCR. It is essential for determining when to start treatment and for monitoring treatment response. Results are reported in Log IU/mL.
Liver function is evaluated using AST/ALT, platelet count, albumin, PT-INR, and other parameters. FibroScan or liver biopsy may also be used to assess the degree of fibrosis progression.
Unlike hepatitis C, the goal of hepatitis B treatment is long-term suppression of viral replication, not complete eradication of the virus. Because HBV-DNA is integrated as cccDNA inside the nucleus of hepatocytes, a true cure is currently difficult. However, achieving functional cure with loss of HBsAg is possible in some cases.
In Japan, NA therapy and interferon therapy for hepatitis B are covered by the Hepatitis Treatment Promotion Program. Depending on household income, patients can continue treatment with a monthly out-of-pocket cost of 10,000 or 20,000 yen.
When a patient is HBsAg-positive but has normal liver function, low HBV-DNA, and no fibrosis, the standard approach is monitoring every 6 to 12 months rather than starting treatment. The timing of treatment initiation should be discussed with a physician based on age, family history, and degree of fibrosis.
The risks of leaving hepatitis B untreated vary depending on the age at infection, whether chronic carriage develops, and host immunity.
1-2% of acute hepatitis B cases progress to fulminant hepatitis. Fulminant hepatitis is an extremely severe condition with a fatality rate of 60-80%, and liver transplantation is sometimes the only life-saving option. Once impaired consciousness appears, immediate transfer to a specialist facility is required.
Chronic hepatitis B progresses to liver cirrhosis at an annual rate of 2-10%, and from cirrhosis the annual rate of HCC development is 2-5%. Approximately 15% of liver cancers in Japan are attributable to hepatitis B.
Even when HBsAg is negative, people with positive anti-HBc (past infection) are at risk of HBV reactivation when given immunosuppressants or chemotherapy. Because reactivation carries a high risk of fulminant hepatitis, HBV screening before chemotherapy and prophylactic NA therapy are now considered standard practice.
An effective preventive vaccine exists for hepatitis B. This is a major difference from hepatitis C.
At Men’s Care Clinic, hepatitis B testing, diagnosis, and vaccination, as well as referrals to specialist hepatology facilities when needed, are all provided in a calm, men’s-only clinical environment.
“My health checkup showed HBsAg positive.” “My partner was diagnosed as a carrier.” “I want to get vaccinated.” Whatever your concern, please feel free to contact us.
Hepatitis B testing and vaccination | Free initial consultation, men’s-only clinic, three locations, free LINE consultation
*A physician will guide you on testing and vaccination plans and costs. *LINE guidance is not a medical diagnosis.
For adult primary infections, more than 90% resolve spontaneously, with HBsAg disappearing and anti-HBs and anti-HBc appearing (a “past infection” pattern). Less than 10% progress to chronic carriage, and about 1-2% develop fulminant hepatitis. In children under 3 years of age, whose immune systems are still immature, the chronic carrier rate rises above 90%.
The standard regimen is three doses at 0, 1, and 6 months. Protective efficacy after the full series is approximately 95%. After completing the series, anti-HBs titer is measured, and 10 mIU/mL or higher is considered protective. In low responders, additional booster doses often raise the antibody titer to protective levels.
Studies report that 30-60% of partners of HBsAg-positive carriers become infected through unprotected sex. Condom use is essential, and if the partner is anti-HBs negative, HBV vaccination is strongly recommended. In the event of exposure, HBIG (hepatitis B immune globulin) combined with vaccination can prevent infection (ideally within 72 hours of exposure).
For inactive carriers with normal liver function, low HBV-DNA, and no fibrosis, the standard approach is observation every 6 to 12 months rather than immediate treatment. The decision to initiate therapy is based on age, family history, degree of fibrosis, and HBeAg status. Regular follow-up with a specialist is essential.
Because HBV-DNA is integrated into hepatocyte nuclei as cccDNA, full eradication of the virus (virologic cure) is currently difficult. However, achieving HBsAg loss (functional cure) is possible in some patients, and clinical development of new agents (capsid inhibitors, siRNA, therapeutic vaccines, etc.) is progressing.
Hepatitis B is commonly transmitted through sexual contact and perinatal exposure, is preventable by vaccine, and has a high spontaneous clearance rate in adult infection. Hepatitis C is primarily bloodborne, has no vaccine, and has a high chronicity rate, but can be cured with DAA (direct-acting antiviral) therapy. For more details, see our article on hepatitis C.
HBV is not transmitted through ordinary meals, handshakes, hugging, or sharing toilets. However, HBV can be present in saliva, and oral contact involving bleeding (such as deep kisses or bites) has been reported to carry transmission risk. In households, avoiding the sharing of toothbrushes, razors, and nail clippers is recommended.
An established mother-to-child transmission prevention protocol exists. Administering HBV vaccine immediately after birth and at 1 and 6 months, together with HBIG (hepatitis B immune globulin) immediately after birth, reduces perinatal transmission by more than 90%. If HBsAg positivity is identified during early pregnancy, coordinated management with the obstetrics department is necessary.
Mild elevation of AST/ALT can have many causes, including fatty liver, alcohol-related liver disease, drug-induced liver injury, viral hepatitis (B or C), and autoimmune hepatitis. If risk behaviors are present, HBsAg and HCV antibody testing are important to screen for and identify the cause.
Initial screening and vaccination can be handled at an STI clinic or general internal medicine clinic. If HBsAg positivity is identified, further evaluation and treatment should be carried out at a gastroenterology or hepatology specialty facility. Men’s Care Clinic provides integrated initial testing, vaccination, and referral to specialist hepatology facilities.
Hepatitis B is a highly infectious disease that is preventable by vaccination. Adult infection has a high spontaneous clearance rate, but once chronic carriage develops, the risk of progression to chronic hepatitis, cirrhosis, and HCC remains. The three pillars of prevention are HBV vaccination, condom use, and avoiding close contact with HBV carriers.
Even when infection is confirmed, long-term suppressive therapy with nucleoside/nucleotide analogs has significantly improved prognosis. Early detection and timely initiation of appropriate treatment are key to preventing HCC.
Related articles: Hepatitis C treatment and risks of leaving it untreated / Comprehensive guide to STIs in men: symptoms and types
Hepatitis B testing, 3-dose vaccination, and treatment coordination | Free initial consultation, men’s-only clinic, available at Shinbashi, Akihabara, and Omotesando
LINEConsult about hepatitis B vaccination
*Available at our Shinbashi, Akihabara, and Omotesando clinics. Online inquiries also accepted. *LINE guidance is not a medical diagnosis.
This article has been prepared under the supervision of Men’s Care Clinic physicians. It provides accurate, evidence-based information, but for any individual symptoms or treatment please consult a physician directly.
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