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