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 Vaccination Schedule 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 month of age (option B). 1

Complete Vaccination Schedule for Infants Born to HBsAg-Positive Mothers

The CDC-recommended vaccination schedule for these high-risk infants includes:

1. First dose: At birth (within 12 hours of life), along with HBIG at a different injection site 1, 2
2. Second dose: At 1-2 months of age 1
3. Third dose: At 6 months of age 1

For infants weighing less than 2,000 grams at birth, a 4-dose schedule is recommended:

• Birth
• 1 month
• 2-3 months
• 6 months 1

Important Clinical Considerations

Administration Details

• Only monovalent hepatitis B vaccine should be used for the birth dose 1
• HBIG (0.5 mL) should be administered intramuscularly to the newborn preferably within 12 hours of birth 2
• HBIG efficacy decreases markedly if treatment is delayed beyond 48 hours 2
• The first dose of vaccine may be given concurrently with HBIG but at a separate injection site 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, 3
• Testing should include both HBsAg and anti-HBs levels 1
• Testing should not be performed before 9 months to avoid detection of passive antibodies from HBIG 1

Common Pitfalls to Avoid

1. Delayed second dose: Research suggests that delaying the second dose beyond 10 weeks increases the risk of chronic HBV infection by 3.74 times in infants born to chronically HBV infected mothers 4

2. Inadequate follow-up: Ensure completion of the full vaccine series and appropriate serological testing to confirm protection 1

3. Communication gaps: When infants are transferred between facilities, clear communication about vaccination and HBIG status is essential to prevent errors 1

4. Low birth weight considerations: Infants with birth weights <2000g have lower seroprotection rates when vaccinated in the first few days of life compared to those vaccinated at 1 month or older (68% vs. 95%) 5

The timely administration of both HBIG and the complete hepatitis B vaccine series is critical for preventing perinatal HBV transmission and the development of chronic hepatitis B infection in these high-risk infants.