Genevac-B Adult Dosing and Administration
For adults ≥20 years of age, Genevac-B (Engerix-B) is administered as 20 mcg (1.0 mL) intramuscularly in the deltoid muscle on a 3-dose schedule at 0,1, and 6 months. 1
Dosing Schedule
Standard Adult Regimen (≥20 years)
- Dose: 20 mcg (1.0 mL) per injection
- Schedule: 0,1, and 6 months (standard)
- Alternative schedule: 0,1,2, and 12 months for rapid protection needs (e.g., recent exposure, high-risk travelers) 1
Special Populations
Hemodialysis and Immunocompromised Adults (≥20 years)
- Dose: 40 mcg (2.0 mL) - given as two 20 mcg injections
- Schedule: 4 doses at 0,1,2, and 6 months
- Important: Annual antibody testing required; give 40 mcg booster when anti-HBs falls below 10 mIU/mL 1
Pregnant Women
- Engerix-B (Genevac-B) is specifically recommended for pregnant women needing hepatitis B vaccination, as newer vaccines (Heplisav-B, PreHevbrio) lack sufficient pregnancy safety data 2
Route of Administration
Intramuscular injection in the deltoid muscle is the standard route 1. Key technical points:
- Never inject intravenously, intradermally, or in the gluteal region - gluteal injection results in suboptimal response 1
- Use 1-inch, 23-gauge needle for adults
- Subcutaneous administration may be used only for patients at hemorrhage risk (e.g., hemophiliacs), but this results in lower antibody titers and increased local reactions including subcutaneous nodules 1
Indications
Universal Recommendation
All adults aged 19-59 years should receive hepatitis B vaccination, regardless of risk factors 2. This 2022 ACIP update removes the need for risk factor screening and disclosure, simplifying vaccination efforts.
Adults ≥60 Years
- Those with risk factors for hepatitis B should be vaccinated
- Those without known risk factors may receive vaccination 3
High-Priority Groups
- Healthcare workers and others with occupational exposure
- Persons with chronic liver disease (including hepatitis C)
- Persons on hemodialysis
- Travelers to endemic areas
- Persons with multiple sexual partners or recent STI
- Household contacts of HBsAg-positive persons
- Persons who inject drugs
Contraindications and Precautions
Absolute Contraindications:
- Severe allergic reaction to any vaccine component or previous dose
- Hypersensitivity to yeast (vaccine produced in Saccharomyces cerevisiae) 1
Special Considerations:
- No substances of human origin used in manufacture 1
- Contains no more than 5% yeast protein 1
- Formulated without preservatives (thimerosal-free) 1
Important Clinical Pearls
Interrupted Series
If the vaccination schedule is interrupted, do not restart the series 2. Simply continue where you left off:
- Minimum interval between doses 1 and 2: 4 weeks
- Minimum interval between doses 2 and 3: 8 weeks
- Minimum interval between doses 1 and 3: 16 weeks
- Doses given ≤4 days before minimum interval are considered valid 2
Pre-vaccination Testing
Testing is NOT required before vaccination 2. However, if performed, test for:
- HBsAg (current infection)
- Anti-HBs (immunity)
- Anti-HBc (previous/ongoing infection)
Lack of access to testing should never be a barrier to vaccination 2.
Expected Response
- Standard adults: 96% seroprotection rate (anti-HBs ≥10 mIU/mL) at month 7 with GMT of 2,204 mIU/mL 1
- Adults >40 years: Lower response (88% seroprotection) with GMT of 610 mIU/mL 1
- Hemodialysis patients: Only 67% seroprotection with 4-dose regimen 1
Preparation and Storage
- Shake well before use - vaccine forms fine white deposit with clear supernatant on storage 1
- Inspect for particulate matter, discoloration, or vial cracks
- Should appear as slightly turbid white suspension after shaking 1
- Use entire dose; discard any remaining vaccine in single-dose vial 1
Booster Doses
For standard adults, booster doses are not routinely recommended except for hemodialysis patients requiring annual monitoring 1. When indicated, adult booster dose is 20 mcg 1.