When is the second dose of hepatitis B (HB) vaccine administered to an infant born to a hepatitis B surface antigen (HBsAg)-positive mother?

Hepatitis B Vaccine Administration for Infants Born to HBsAg-Positive Mothers

The second dose of hepatitis B vaccine for an infant born to an HBsAg-positive mother should be administered at 1-2 months of age. 1

Comprehensive Vaccination Schedule for Infants Born to HBsAg-Positive Mothers

The complete vaccination and prophylaxis regimen for these high-risk infants includes:

1. At birth (within 12 hours):

   • Hepatitis B vaccine (first dose) - monovalent formulation only
   • Hepatitis B immune globulin (HBIG) 0.5 mL - administered at a different injection site 1, 2, 3

2. At 1-2 months of age:

   • Hepatitis B vaccine (second dose) 1

3. At 6 months of age:

   • Hepatitis B vaccine (third dose) 1

Important Clinical Considerations

Timing is Critical

The timing of the second dose at 1-2 months is crucial for developing protective immunity. Research shows that delayed second doses (beyond 10 weeks) increase the risk of chronic HBV infection by 3.74 times in infants born to HBV-infected mothers 4.

Special Weight Considerations

For infants weighing <2,000 grams at birth:

• The birth dose should not be counted as part of the vaccine series
• A total of 4 doses should be administered (at birth, 1 month, 2-3 months, and 6 months) 1, 2

Follow-up Testing

• Postvaccination serologic testing (PVST) should be performed at age 9-12 months (or 1-2 months after the final vaccine dose if delayed) 1, 5
• Testing should include both HBsAg and anti-HBs levels
• Testing should not be performed before 9 months to avoid detection of passive antibodies from HBIG 1

Vaccine Efficacy

The complete regimen of HBIG plus timely hepatitis B vaccination is highly effective at preventing perinatal HBV transmission. Studies show that this approach reduces the risk of chronic HBV infection from approximately 73% to less than 7% in infants born to HBsAg-positive mothers 6.

Common Pitfalls to Avoid

1. Using combination vaccines for the birth dose: Only monovalent hepatitis B vaccine should be used for the birth dose 1, 2

2. Delaying the second dose: Ensure the second dose is administered at 1-2 months, as delays increase infection risk 4

3. Failing to communicate during hospital transfers: When infants are transferred to different facilities, staff must communicate regarding the infant's HepB vaccination and HBIG receipt status 1, 2

4. Premature testing: Testing before 9 months of age may detect passive antibodies from HBIG rather than true vaccine-induced immunity 1, 5

5. Inadequate follow-up: Ensure that infants complete the full vaccine series and receive appropriate serologic testing 1, 2

The answer to the question is B. 1 month, as the second dose of hepatitis B vaccine for an infant born to an HBsAg-positive mother should be administered at 1-2 months of age.