1. Clinical Overview
Hepatitis B Vaccine (rDNA) is a sterile suspension containing the Hepatitis B surface antigen (HBsAg) produced by recombinant DNA technology in yeast cells (*Saccharomyces cerevisiae*). The 20 mcg dose is the standard adult formulation used for active immunization against infection caused by all known subtypes of the Hepatitis B virus. It induces the production of specific anti-HBs antibodies, providing protection against acute and chronic hepatitis B, cirrhosis, and hepatocellular carcinoma.
| Onset | Duration | Bioavailability |
|---|---|---|
| Protective antibody titers (≥10 mIU/mL) typically develop in 90-95% of healthy adults within 1-2 months after completing the primary 3-dose series. | Long-term, potentially lifelong protection in individuals who mount an adequate initial immune response (anti-HBs ≥10 mIU/mL). Memory B-cells provide long-term immunity even if antibody titers wane below detectable levels. | Not applicable (Parenteral administration). Immunogenicity is the relevant measure, not classical bioavailability. |
2. Mechanism of Action
The vaccine contains the Hepatitis B surface antigen (HBsAg) adsorbed onto aluminum hydroxide adjuvant. Upon intramuscular injection, the antigen is taken up by antigen-presenting cells (APCs) at the site and in draining lymph nodes. APCs process and present HBsAg peptides on Major Histocompatibility Complex (MHC) class II molecules to CD4+ T-helper cells. Activated T-helper cells stimulate antigen-specific B-lymphocytes to proliferate and differentiate into plasma cells, which secrete protective anti-HBs antibodies (IgG). Memory B-cells and T-cells are also generated, providing long-term immunity.
3. Indications & Uses
- Active immunization against infection caused by all known subtypes of Hepatitis B virus.
- Pre-exposure prophylaxis for individuals at increased risk of HBV infection.
- Post-exposure prophylaxis (along with Hepatitis B Immunoglobulin) for percutaneous/permucosal exposure to HBsAg-positive materials.
4. Dosage & Administration
Adult Dosage: 20 mcg (1.0 mL) intramuscularly, as a 3-dose schedule at 0, 1, and 6 months. An alternative 0, 1, 2, and 12-month schedule can be used for rapid induction.
Administration: Shake vial/syringe well before use. Administer by intramuscular injection into the deltoid muscle in adults and older children. The anterolateral thigh is preferred for infants. Do NOT inject intravenously, intradermally, or subcutaneously (can reduce immunogenicity). Use a separate, sterile syringe and needle for each individual.
5. Side Effects
Common side effects may include:
- Pain, tenderness, erythema, and induration at the injection site (15-25%).
- Low-grade fever (<101°F), malaise, fatigue, headache (1-10%).
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Immunosuppressants (e.g., high-dose corticosteroids, chemotherapy, biologics) | Diminished immunogenic response; may not achieve protective antibody titers. | Major |
| Other Vaccines (e.g., DPT, OPV, IPV, Hepatitis A) | Can be administered simultaneously at different sites without interference. Immune response may be slightly reduced for some co-administered antigens but remains protective. | Moderate |
| Hepatitis B Immunoglobulin (HBIG) | Can be administered simultaneously at a different site for post-exposure prophylaxis without affecting active immunity. | None |
7. Patient Counselling
- Do complete the full 3-dose schedule for long-term protection.
- Do inform the doctor about any severe allergies, especially to yeast.
- Do keep the vaccination record card safe.
- Don't skip doses; if a dose is delayed, resume the schedule; no need to restart.
- Don't apply pressure or massage the injection site vigorously.
8. Toxicology & Storage
Overdose: Unlikely due to fixed-dose vial/syringe. Potential symptoms would be similar to exaggerated local reactions (severe pain, swelling) or systemic reactions (high fever, malaise).
Storage: Store between +2°C to +8°C in a refrigerator. Do not freeze. Protect from light. Frozen vaccine which has been thawed should NOT be used. Keep in original pack until use. Use immediately after opening the vial. Do not use after expiry date.