Challenge with a hepatitis B vaccine in two cohorts of 4–7-year-old children primed with hexavalent vaccines: An open-label, randomised trial in Italy

Background and aimsThe anamnestic response to a challenge dose of vaccine can assess immune memory and protection against hepatitis B infection. This study investigated responses to a challenge dose of monovalent hepatitis B vaccine in children immunised with three doses of either Hexavac or Infanrix-Hexa during infancy.MethodsThis open-label, randomised, controlled, four-arm study enrolled 410 healthy children aged 4–7 years who had received either Hexavac (n = 201) or Infanrix-Hexa (n = 209) at 3, 5 and 11 months of life. Children received a single intramuscular challenge dose of either hepatitis B vaccine, HBVaxPro (Hexavac, n = 34; Infanrix-Hexa, n = 28) or Engerix-B (Hexavac, n = 167; Infanrix-Hexa, n = 181). Hepatitis B surface antibody (anti-HBs) concentrations were measured before and 1 month after the challenge vaccine dose. The analysis was descriptive and no formal hypothesis was tested.ResultsOne month post-challenge, 91.2% of children in the Hexavac group (95% confidence interval [CI] 86.3, 94.8) and 98.0% (95% CI 94.9, 99.4) in the Infanrix-Hexa group had anti-HBs concentrations ≥10 mIU/ml (primary endpoint). In a post hoc analysis, most children with pre-challenge anti-HBs concentration <10 mIU/ml achieved anti-HBs concentrations ≥10 mIU/ml (Hexavac group, 85.3% [95% CI 77.6, 91.2]; Infanrix-Hexa group, 91.9% [95% CI 78.1, 98.3]). Both challenge vaccines were well tolerated.ConclusionsThese data suggest that immune memory persists for long-term (5 years) after a primary vaccination in infancy with a hexavalent vaccine (Hexavac or Infanrix-Hexa).

► Post-challenge anti-HBs ≥10 mIU/ml occurred in >90% of all children.
► Post/pre-challenge anti-HBs GMCR were comparable in all children.
► Post-challenge anti-HBs ≥10 mIU/ml was >85% of children with <10 mIU/ml pre-challenge.
► Post-challenge anti-HBs GMC were comparable in children with <10 mIU/ml pre-challenge.
► The immune responses did not differ between HBVaxPro and Engerix-B challenge dose.