Can a child who has received the Hepatitis B (HB) vaccine and Hepatitis B Immunoglobulin (HBIG) still get a Hepatitis B surface antigen (HBsAg) infection?

Can a Hepatitis B Vaccinated and HBIG Administered Child Still Get HBsAg Infection?

Yes, but the risk is extremely low at 5-15% when both HepB vaccine and HBIG are administered within 12 hours of birth to infants born to HBsAg-positive mothers, with the vast majority (85-95%) being protected from chronic HBV infection. 1

Efficacy of Combined Prophylaxis

The combination of HBIG and hepatitis B vaccine administered within 12 hours of birth provides highly effective protection:

• Passive-active postexposure prophylaxis (PEP) is 85-95% effective in preventing both acute and chronic HBV infection in infants born to mothers who are positive for both HBsAg and HBeAg 1
• The remaining 5-15% of infants may still develop HBV infection despite appropriate prophylaxis 1
• Protection rates are comparable (98.5% vs 98.2%) whether 100 IU or 200 IU of HBIG is used at birth 2

Factors Affecting Prophylaxis Failure

Maternal HBeAg status is the strongest predictor of prophylaxis failure:

• Infants born to HBeAg-positive mothers have a 9.26% chronic infection rate despite complete immunization, compared to only 0.29% for infants born to HBeAg-negative mothers 3
• The rate of HBV infection markers (anti-HBc positivity) is significantly higher in children of HBeAg-positive mothers (16.76%) versus HBeAg-negative mothers (1.58%) 3
• Among infected children, chronicity rates are also higher with HBeAg-positive mothers (54%) versus HBeAg-negative mothers (17%) 3

Timing and Administration Critical Points

The effectiveness of prophylaxis is highly time-dependent:

• Both HBIG and vaccine must be administered within 12 hours of birth at different anatomical sites (e.g., separate limbs) 1
• HBIG may provide some protection when administered up to 72 hours after birth, but efficacy diminishes with delayed administration 1
• The effectiveness of PEP is unlikely to exceed 7 days for perinatal exposures 1

Special Considerations for Preterm Infants

Infants weighing <2,000 grams require modified dosing:

• The birth dose should not be counted as part of the vaccine series due to potentially reduced immunogenicity 1
• These infants require 4 total doses of vaccine (birth dose plus 3 additional doses starting at 1 month of age) 1
• Both HBIG and vaccine should still be administered within 12 hours of birth 1

Post-Vaccination Testing Requirements

Mandatory serologic testing identifies prophylaxis failures:

• Testing for anti-HBs and HBsAg should be performed at age 9-12 months (generally at the next well-child visit after completing the vaccine series) 1
• Testing should not be performed before 9 months to avoid detecting passive anti-HBs from HBIG and to maximize detection of late HBV infection 1
• HBsAg-negative infants with anti-HBs ≥10 mIU/mL are protected and need no further management 1
• HBsAg-negative infants with anti-HBs <10 mIU/mL should be revaccinated 1
• HBsAg-positive infants represent prophylaxis failures and require appropriate follow-up for chronic HBV infection 1

Intrauterine Infection

A small percentage of infections occur in utero and cannot be prevented by birth prophylaxis:

• Probable intrauterine HBV infections have been documented in infants who test HBsAg-positive at 1 month of age despite receiving HBIG and vaccine at birth 4, 5
• These infants are considered to have acquired infection prenatally, before prophylaxis could be administered 5
• Even in these cases, continuing the vaccination program may alter immune tolerance and lead to HBeAg seroconversion in approximately 33% of cases 5

Long-Term Protection in Immunocompetent Children

Children who respond to the vaccine series maintain long-term protection:

• Among fully immunized children with leukemia receiving immunosuppressive therapy, the HBV breakthrough infection rate was only 0.98% (4/410 children) 6
• This demonstrates that even in immunocompromised states, neonatal hepatitis B vaccination confers substantial protection 6

Common Pitfalls to Avoid

• Do not delay HBIG or vaccine administration beyond 12 hours of birth—efficacy decreases significantly with time 1
• Do not skip post-vaccination testing at 9-12 months, as this is the only way to identify prophylaxis failures who need follow-up 1
• Do not count the birth dose in preterm infants <2,000g as part of the vaccine series—they need 4 total doses 1
• Do not test before 9 months of age, as passive antibodies from HBIG will confound results 1