Hepatitis A Immunity After Twinrix Vaccination

Understanding Hepatitis A Antibody Testing

The Centers for Disease Control and Prevention recommends using a total anti-HAV antibody test to determine hepatitis A immunity after Twinrix vaccination, with a positive result indicating protection 1
Antibody concentrations achieved after Twinrix vaccination are 10-100 fold lower than those produced after natural infection and may be below the detection limit of some commercial assays 1
Standard commercial immunoassays typically have a lower detection limit of approximately 100 mIU/mL, while more sensitive assays used in research settings can detect levels as low as 10 mIU/mL 1
Anti-HAV antibody concentrations are measured in comparison with a World Health Organization reference immunoglobulin reagent and expressed as milli-International Units per milliliter (mIU/mL) 1

A positive anti-HAV result by a standard commercial assay definitively indicates protection against hepatitis A 1
Vaccinated individuals who test negative by standard assays might still have protective levels of antibody that are below the detection threshold 1
Clinical studies have used different thresholds to define protective antibody response, including levels >20 mIU/mL or >33 mIU/mL for HAVRIX and levels >10 mIU/mL for VAQTA 1

The Centers for Disease Control and Prevention recommends testing for hepatitis A immunity 1-2 months after completing the full vaccination series 2
For Twinrix, this would be 1-2 months after the third dose (given at 0, 1, and 6 months) 1

Routine testing for hepatitis A immunity after vaccination is generally not recommended due to high seroconversion rates (97-100% in adults after completing the series) 3, 4
The American Academy of Pediatrics notes that the insensitivity of standard commercial assays to detect vaccine-induced immunity is a reason to avoid routine testing 4

Testing might be considered for immunocompromised individuals or those with chronic liver disease, who may have lower seroconversion rates 4
If testing is performed and results are negative by standard assay, this does not necessarily indicate lack of protection 1
Antibody levels after vaccination with Twinrix are comparable to those achieved with single-antigen vaccines administered separately 1

Using insensitive assays that may miss protective antibody levels induced by vaccination 1
Misinterpreting a negative test result as indicating lack of protection when the individual may still have protective levels below the assay's detection threshold 1
Testing too soon after vaccination before peak antibody levels have developed 2
Unnecessary testing in immunocompetent individuals who have completed the full vaccination series 4