HBV vaccination and prevention

HBV Vaccine Basics - The Viral Shield

• Type: Recombinant DNA, subunit vaccine.
• Composition: Pure Hepatitis B surface antigen (HBsAg).
  • Does not contain live or killed virus.
• Production: Synthesized by yeast (Saccharomyces cerevisiae) genetically engineered to express the HBsAg gene.
• Mechanism: Stimulates production of neutralizing anti-HBs antibodies, conferring active immunity.

⭐ Because the vaccine contains only HBsAg (a non-infectious viral protein), it is impossible to get hepatitis B from the vaccine itself.

Immunization Schedule - Sticking to the Point

• Universal Neonatal Vaccination: All infants should receive the first dose at birth, regardless of maternal HBsAg status.
• Standard 3-Dose Series: Administered at 0, 1, and 6 months.
  • Route: Intramuscular (IM) injection, typically in the deltoid muscle for adults and anterolateral thigh for infants.
• High-Risk Adult Vaccination: Indicated for healthcare workers, patients with chronic kidney disease (CKD) or chronic liver disease, IV drug users, and household contacts of individuals with HBV infection.

⭐ For infants born to HBsAg-positive mothers, administer both the HBV vaccine and Hepatitis B Immune Globulin (HBIG) within 12 hours of birth to prevent perinatal transmission.

Serologic Interpretation - Reading the Signs

Interpreting Hepatitis B serology is key to diagnosing infection status and determining immunity. The main markers are HBsAg, anti-HBs, and anti-HBc.

📌 Mnemonic: 'Ag' = Always Growing (infection). 'Anti-c' = Caught it (core Ab). 'Anti-s' = Safe/Shot (surface Ab).

• Infectivity: Presence of HBsAg indicates the virus is replicating and the individual is infectious. HBeAg (not shown) is a marker of high infectivity.

⭐ Exam Favorite: During the "window period," both HBsAg and anti-HBs may be negative. The only positive marker is anti-HBc IgM, making it crucial for diagnosing acute infection in this phase.

Post-Exposure Prophylaxis - After the Accident

Management hinges on the source's HBsAg status and the exposed person's vaccination and antibody status. The goal is to provide passive immunity (HBIG) and active immunity (vaccine).

• Perinatal Exposure: For an infant born to an HBsAg+ mother, give Hepatitis B Immune Globulin (HBIG) and the first dose of the HBV vaccine within 12 hours of birth.

⭐ A vaccine "non-responder" is someone with persistently low anti-HBs levels (<10 mIU/mL) despite receiving two complete 3-dose vaccine series. Their post-exposure management is distinct.

High‑Yield Points - ⚡ Biggest Takeaways

• The HBV vaccine is a safe, effective recombinant vaccine containing HBsAg.
• It induces protective anti-HBs antibodies in >95% of recipients, forming the mainstay of prevention.
• Post-exposure prophylaxis combines HBV vaccine and Hepatitis B Immune Globulin (HBIG).
• Infants of HBsAg-positive mothers must receive the vaccine and HBIG within 12 hours of birth.
• Routine screening of all pregnant women for HBsAg is a critical prevention strategy.