Why is the Hepatitis B (HepB) vaccine recommended for infants?

Why Hepatitis B Vaccine is Recommended for Infants

All infants should receive the hepatitis B vaccine series beginning at birth as a critical safety net to prevent perinatal transmission, chronic infection, and the devastating long-term consequences of cirrhosis and hepatocellular carcinoma. 1

Primary Rationale: Prevention of Perinatal Transmission and Chronic Disease

The birth dose serves as essential protection against vertical transmission, which is the primary mode of hepatitis B virus (HBV) acquisition in endemic areas and accounts for approximately 50% of chronic infection cases globally. 2

Risk of Chronic Infection Without Vaccination

• Infants infected perinatally have a 90% risk of becoming chronic HBV carriers if born to mothers who are both HBsAg and HBeAg-positive and receive no immunoprophylaxis. 2
• Infection during infancy leads to chronic carriage in 25-90% of cases, compared to only 5-10% when infection occurs during adulthood. 2
• Chronic HBV infection acquired in infancy carries lifelong risk of developing cirrhosis and hepatocellular carcinoma (HCC), with HBV causing an estimated 620,000 deaths annually worldwide. 3

Universal Vaccination Strategy: The Safety Net Approach

The Advisory Committee on Immunization Practices recommends universal infant vaccination beginning at birth, regardless of maternal HBsAg status, as a critical safety net. 1

Why the Birth Dose is Critical

• For medically stable infants ≥2,000 grams born to HBsAg-negative mothers, the first dose should be administered within 24 hours of birth. 1
• This timing is essential because maternal HBsAg status may be unknown, incorrectly documented, or testing may be falsely negative, making universal birth dosing the only reliable prevention strategy. 1
• In areas with ≥8% chronic HBV prevalence, WHO specifically recommends the birth dose within 24 hours to prevent perinatal transmission. 3

Protection Against Unknown Maternal Status

• Infants born to mothers with unknown HBsAg status (≥2,000 grams) should receive HepB vaccine within 12 hours of birth while maternal testing is expedited. 1
• If maternal status cannot be determined (e.g., safely surrendered infants), the complete vaccine series should follow the schedule for infants born to HBsAg-positive mothers, with postvaccination serologic testing at 9-12 months. 1

Proven Long-Term Efficacy and Population Impact

Real-world evidence from Taiwan's universal infant vaccination program, launched in 1984, demonstrates dramatic reductions in chronic HBV infection, HCC incidence, and fulminant hepatitis in children. 2

Evidence of Disease Prevention

• Vaccination with HepB vaccine alone prevents the persistent carrier state in 79% of at-risk infants (21% carrier rate versus 73.2% in controls), even without hepatitis B immunoglobulin. 4
• When combined with HBIG at birth, protection increases to 97.1% (2.9% carrier rate), demonstrating near-complete prevention of chronic infection. 4
• Population-based trials in high-endemicity regions show long-lasting protection against chronic carriage and expected dramatic decreases in chronic liver disease and liver cancer within decades of implementation. 5

Immunologic Basis for Infant Vaccination

Immunologic memory persists for 30 years or more in vaccine responders, even when antibody levels decline below the protective threshold of 10 mIU/mL. 6

Long-Term Protection Mechanisms

• 88% of individuals who received the complete 3-dose series as children develop an anamnestic response when given a challenge dose 30 years later, indicating persistent cellular immunity. 6
• Protection against chronic infection continues despite declining antibody levels, with data showing protection persists for ≥30 years among immunocompetent individuals who originally responded to vaccination. 6
• Antibody decline is expected and normal: only 16% of those vaccinated at age <1 year maintain anti-HBs ≥10 mIU/mL at 18 years, compared to 74% for those vaccinated at age ≥1 year, but this does not indicate loss of protection. 6

Practical Implementation Guidelines

The complete infant vaccination series consists of 3-4 doses depending on maternal HBsAg status, with specific timing requirements to ensure optimal immunogenicity. 1

Standard Vaccination Schedule

• For infants born to HBsAg-negative mothers: Birth dose, followed by completion of the series with the final dose not administered before age 24 weeks (164 days). 1
• For infants born to HBsAg-positive mothers: HepB vaccine plus HBIG within 12 hours of birth at different injection sites, with completion of the series and postvaccination serologic testing at 9-12 months. 1
• For low birth weight infants (<2,000 grams) born to HBsAg-positive mothers: The birth dose does not count toward the series; administer 3 additional doses (total of 4) beginning at age 1 month. 1

Special Populations Requiring Enhanced Surveillance

• In populations with high rates of childhood HBV infection (Alaska Natives, Pacific Islanders, immigrant families from Asia/Africa), the first dose should be administered at birth with the final dose at 6-12 months. 1
• Infants weighing <2,000 grams born to HBsAg-negative mothers should delay the first dose until hospital discharge or age 1 month, as they have decreased vaccine response before 1 month of age. 1

Critical Pitfalls to Avoid

Never assume maternal HBsAg status is accurate without verification, as documentation errors, false-negative results, or acute maternal infection can occur between testing and delivery. 1

Never delay the birth dose beyond 24 hours for eligible infants, as timing is critical for preventing perinatal transmission, particularly when maternal status is unknown or positive. 1, 3

Never count the birth dose in low birth weight infants (<2,000 grams) born to HBsAg-positive mothers as part of the vaccine series due to reduced immunogenicity; these infants require 4 total doses. 1