Is hepatitis B vaccination performed at infant and adolescent age able to provide long-term immunological memory? An observational study on healthcare students and workers in Florence, Italy.

Universal vaccination programmes against Hepatitis B Virus (HBV) have significantly reduced the burden of the disease; nevertheless, HBV infection remains a relevant issue for high-risk subjects, such as healthcare workers (HCWs), who may potentially be exposed to blood or body fluids. Our study evaluates the long-term duration of the immunological memory of HBV vaccination 11-23 years after primary immunization by examining the response to booster doses in HCWs and students of health disciplines at Careggi Teaching Hospital in Florence (Italy). All participants (n = 2,203) had received a complete HBV immunization course in infancy or adolescence. Blood samples were collected to measure antibody levels against the HBV surface antigen (anti-HBs); an anti-HBs titre <10 mIU/mL was considered as negative. The administration of the vaccination course during infancy induced lower long-term anti-HBs titres compared to those in case of vaccination performed during adolescence (titre <10 mIU/mL: 51.1% and 12.2% respectively; p < 0.001), also considering that an equal number of years has elapsed since vaccination. A booster dose administered to subjects vaccinated in infancy is able to induce anamnestic immunological response in a higher percentage of vaccinated people (p < 0.001). Few subjects (n. = 4) accepted a fifth dose of vaccine in the case of persistent anti-HBs negative titres; this aspect requires further investigation. The total absence of acute hepatitis B among vaccinated subjects suggests that the long incubation period of the disease allows the activation of immunologic memory mechanisms, which is also true in case of low anti-HBs level. In conclusion HCWs still represent a high-risk category; it is therefore, necessary to increase efforts to protect and vaccinate these subjects.