Persistence of immunity 18-19 years after vaccination against hepatitis B in 2 cohorts of vaccinees primed as infants or as adolescents in Italy.

This study was aimed at assessing the anti-HBs persistence and immune memory 18-19 y after vaccination against hepatitis B in healthy individuals primed as infants or adolescents. We enrolled 405 teenagers (Group A) vaccinated as infants, and 409 young adults (Group B) vaccinated as adolescents. All vaccinees were tested for anti-HBs and anti-HBc antibodies; those found anti-HBc positive were further tested for HBsAg and HBV DNA. Eight individuals belonging to Group B were positive for anti-HBc alone, and were excluded from analysis. Individuals with anti-HBs concentration ≥ 10 mIU/ml were considered protected while those with anti-HBs concentration <10 mIU/ml were offered a booster dose and re-tested 2 weeks later. Overall, 67.9% individuals showed anti-HBs concentrations ≥ 10 mIU/ml (48.9% in Group A vs 87.0% in Group B, p < 0.001). The antibody geometric mean concentration (GMC) was higher in Group B than in Group A (102.5 mIU/ml vs 6.9 mIU/ml; p < 0.001). When boosted, 94.2% of vaccinees with anti-HBs <10 mIU/ml belonging to Group A and 94.7% to Group B showed an anamnestic response. Post-booster GMCs were similar in both groups (477.9 mIU/ml for Group A vs 710.0 mIU/ml for Group B, p = n.s.). Strong immunological memory persists for at least 18-19 y after immunization of infants or adolescents with a primary course of vaccination. Thus, booster doses are not needed at this time, but additional follow up is required to assess the long-life longevity of protection.

Long-term immunogenicity of hepatitis B vaccination and policy for booster: an Italian multicentre study.

BACKGROUND: Universal anti-hepatitis-B vaccination of infants and adolescents was implemented in Italy in 1991. We undertook a multicentre study in previously vaccinated individuals to assess the duration of immunity and need for booster, over 10 years after vaccination. METHODS: In 1212 children and 446 Italian Air Force recruits vaccinated as infants and adolescents, respectively, we measured the concentrations of antibodies to hepatitis-B surface antigen (anti-HBs) and the presence of antibodies to hepatitis-B core antigen (anti-HBc) at enrollment; postimmunisation values were not available. Individuals positive for anti-HBc were tested for hepatitis B surface antigen (HBsAg) and hepatitis B viral DNA. Individuals with anti-HBs concentrations at 10 IU/L or more were regarded as protected; those with antibody less than 10 IU/L were given a booster dose and retested 2 weeks later. Individuals showing postbooster anti-HBs concentrations of less than 10 IU/L were offered two additional vaccine doses and retested 1 month after the third dose. FINDINGS: Protective anti-HBs concentrations were retained in 779 (64%, 95% CI 61.6-67) children and 398 (89%, 86.4-92.1) recruits. We recorded antibody amounts of less than 10 IU/L in 433 children (36%, 33-38.4) and 48 (11%, 7.9-13.6) recruits. One child and four recruits were positive for anti-HBc, but negative for HBsAg and hepatitis B viral DNA. Antibody concentrations were higher in recruits than in children (geometric mean titre 234.8 IU/L vs 32.1 IU/L, p=0.0001). 332 (97%) of 342 children and 46 (96%) of 48 recruits who received a booster showed an anamnestic response, whereas ten (3%) children and two (4%) recruits remained negative for anti-HBs or had antibody concentrations of less than 10 IU/L. Prebooster and postbooster antibody titres were strongly correlated with each other in both groups. All individuals given two additional vaccine doses (eight children and two recruits) showed anti-HBs amounts of more than 10 IU/L at 1 month after vaccination. INTERPRETATION: Strong immunological memory persists more than 10 years after immunisation of infants and adolescents with a primary course of vaccination. Booster doses of vaccine do not seem necessary to ensure long-term protection.