What is the standard dose and dosing schedule of the inactivated hepatitis A vaccine for individuals aged ≥1 year, and how should it be adjusted for rapid protection, immunocompromised patients, or infants?

Hepatitis A Vaccine Dosing

For individuals aged ≥1 year, administer hepatitis A vaccine as a 2-dose series: children 12 months to 18 years receive 0.5 mL (HAVRIX 720 ELU or VAQTA 25 U), and adults ≥19 years receive 1.0 mL (HAVRIX 1440 ELU or VAQTA 50 U), with the second dose given 6-12 months after the first dose. 1

Standard Dosing by Age and Vaccine Type

Children and Adolescents (12 months to 18 years)

• HAVRIX: 0.5 mL containing 720 ELU per dose 1
• VAQTA: 0.5 mL containing 25 U per dose 1
• Schedule: Two doses administered 6-12 months apart (HAVRIX) or 6-18 months apart (VAQTA) 1
• Route: Intramuscular injection into the deltoid muscle 1

Adults (≥19 years)

• HAVRIX: 1.0 mL containing 1440 ELU per dose 1
• VAQTA: 1.0 mL containing 50 U per dose 1
• Schedule: Two doses administered 6-12 months apart (HAVRIX) or 6-18 months apart (VAQTA) 1
• Route: Intramuscular injection into the deltoid muscle 1

Combined Hepatitis A/B Vaccine (Adults ≥18 years only)

• TWINRIX: 1.0 mL containing 720 ELU hepatitis A antigen plus 20 μg hepatitis B antigen 1
• Standard schedule: Three doses at 0,1, and 6 months 1
• Accelerated schedule for rapid protection: Four doses at 0,7, and 21-30 days, followed by a booster at 12 months 2
• Note: TWINRIX is NOT licensed for use in children under 18 years 1

Special Populations and Adjustments

Infants (6-12 months)

While not part of standard recommendations, hepatitis A vaccine can be administered as early as 6 months of age when indicated 3. The pediatric dose (0.5 mL) is used, with the second dose given 6 months later 3. This schedule produces 100% seroconversion rates and is well-tolerated when given alone or concomitantly with other routine childhood vaccines 3.

Immunocompromised Patients

• Use the same standard doses as immunocompetent individuals 1
• Immunocompromising conditions are NOT a contraindication to hepatitis A vaccination because the vaccine contains completely inactivated virus that cannot replicate 1, 4
• The vaccine is safe for immunocompromised persons, though antibody response may be lower than in healthy individuals 1
• Post-vaccination serologic testing is generally not recommended even in immunocompromised patients because commercially available assays may not detect the low but protective antibody levels induced by vaccination 1

Rapid Protection Scenarios

For travelers or others needing immediate protection, a single dose provides 95-97% seroprotection within one month 1. The second dose should still be administered at the recommended interval to ensure long-term protection 1.

Flexible Booster Timing

Evidence demonstrates that the second dose remains highly immunogenic even when delayed significantly beyond the standard 6-12 month interval 1. Booster doses administered up to 10.67 years after the initial dose produce strong immune responses with seroprotection rates of 90-100% 1. The immune memory response is independent of the time interval since initial vaccination 1.

Key Immunogenicity Data

• After first dose: 95-97% of recipients develop protective antibody levels within one month 1
• After second dose: Virtually 100% achieve protection 1
• Interchangeability: The two vaccines (HAVRIX and VAQTA) are interchangeable; the 2-dose series may be completed with either preparation 1
• Concomitant administration: Hepatitis A vaccine can be safely administered simultaneously with DTaP, polio, Hib, hepatitis B, MMR, and other routine childhood vaccines without affecting immunogenicity or safety 1, 3

Critical Pitfalls to Avoid

• Do not restart the series if interrupted—simply administer the remaining dose(s) when the patient returns 1
• Do not perform routine post-vaccination serologic testing because standard commercial assays are not sensitive enough to detect the low but protective antibody levels produced by vaccination 1
• Do not use TWINRIX in children under 18 years—it is only licensed for adults 1
• Do not withhold vaccination from immunocompromised patients—the inactivated vaccine cannot cause infection and is safe in this population 1, 4
• Do not confuse vaccine-induced IgM anti-HAV with acute infection—HAVRIX can induce detectable IgM in 8-20% of adults within 2-3 weeks after vaccination 4

Storage Requirements

Store and ship hepatitis A vaccines at 2-8°C (35.6-46.4°F) 1. Do not freeze, as freezing destroys vaccine potency 1. However, both HAVRIX and VAQTA maintain immunogenicity and reactogenicity even after storage at 37°C (98.6°F) for up to one week 1.