Background: In 2001, two hexavalent vaccines were licensed in Italy (Hexavac®, Infanrix Hexa®), and since 2002 were extensively used for primary immunization in the first year of life (at 3, 5, 11/12 months of age). In 2005, the market authorization of Hexavac® was precautionary suspended by EMEA, because of doubts on long-term protection against hepatitis B virus. The objectives of this study were to evaluate the persistence of antibodies to anti-HBs, in children in the third year of life, and to investigate the response to a booster dose of hepatitis B vaccine. Methods: Participant children were enrolled concomitantly with the offering of anti-polio booster dose, in the third year of life. Anti-HBs titers were determined on capillary blood samples. A booster dose of hepatitis B vaccine was administered to children with anti-HBs titers <10 mIU/ml, with the monovalent precursor product of the previously received hexavalent vaccine. HBsAb titers were tested again one month after the booster. Results: Sera from 113 children previously vaccinated with Hexavac®, and from 124 vaccinated with Infanrix Hexa® were tested for anti-HBs. Titers were ≥ 10 mIU/ml in 69% and 96% (p <0,0001) respectively. The proportion of children with titers ≥ 100 mIU/ml did also significantly differ among groups (27% and 78%; p <0,0001). Post-booster, 93% of children achieved titers ≥ 10 mIU/ml, with no significant difference by vaccine group. Discussion: Fifteen months after third dose administration, a significant difference in anti-HBs titers was noted in the two vaccine groups considered. Monovalent hepatitis B vaccine administration in 3-year old children induced a proper booster response, confirming that immunologic memory persists in children with anti-HBs titers <10 mIU/ ml. However, long-term persistence of HBV protection after hexavalent vaccines administration should be further evaluated over time.
ASJC Scopus subject areas
- Infectious Diseases