Will Infant Hepatitis B Vaccination Protect into Adulthood? Extended Canadian Experience After a 2, 4, 6 Month Immunization Schedule

Hepatitis B virus (HBV) vaccination programs generally target infants to prevent chronic HBV infection and/or pre-adolescents to reduce transmission in adulthood. To assess whether infant HBV immunization can potentially accomplish both objectives we measured residual immunity 10-16 years after vaccination in Canadian children. A prospective, parallel group, single center study enrolled adolescents given HBV vaccine at 2, 4, and 6 months of age. Exclusion criteria included prior HBV infection and additional vaccinations. At follow-up anti-HBs testing participants were 10-11 or 15-16 years old; those with <12 mIU/mL anti-HBs by the assay used were challenged with HBV vaccine to assess immune memory-based responsiveness. 137 tested participants were 10-11 and 213 were 15-16 years old, respectively; none had evidence of prior HBV infection. At baseline, 78% of younger and 64% of older participants had <12 mIU/mL anti-HBs (p=0.006) and were challenged with vaccine: 103/106 (97.2%) younger and 123/135 (91.1%) older participants developed ≥12 mIU/mL anti-HBs (p=0.06), with GMC of 590 (95%CI 473, 737) and 319 mIU/mL (95% CI 229, 445)(p=0.004), respectively. Immune memory loss may have occurred in 3 younger (2.2%) and 12 older children (5.6%) (p=0.06) who were non-responsive to first but not second vaccine challenge. After HBV vaccination at 2, 4, 6 months of age, most adolescents had little or no residual antibody but nearly all responded to HBV challenge, confirming immune memory persistence. However, anamnestic responses were weaker in 15-16 year olds and lost in some. Booster responses in 10-11 year olds were vigorous in comparison. Extended evaluation of protection is warranted.