Impact of the Hepatitis B Immunization Strategy Adopted in Italy from 1991: The Results of a Seroprevalence Study on the Adult Population of Florence, Italy

Italy was one of the first countries to implement a hepatitis B (HBV) immunization strategy in 1991; since its introduction, the epidemiology of this disease has significantly changed. The aim of this retrospective study was to assess the seroprevalence of three HBV markers (anti-HBs, anti-HBc, and HBsAg) and describe the acquired immunity in a representative sample of the adult general population in the province of Florence (Italy) between April 2018 and December 2019. We conducted an enzyme-linked immunosorbent assay on 430 serum samples collected from the adult general population to quantify anti-HBs titers and assess the presence of anti-HBc and HBsAg. For the interpretation of hepatitis B serologic results, we referred to the US CDC guidelines. We conducted two multivariate logistic regression analyses (applied to the entire enrolled population and to the unvaccinated) to assess predictors of immunity against HBV using sex, age, and nationality as predictors. The overall anti-HBs prevalence was 30%, with a significant decreasing trend in seropositivity with increasing age. The overall anti-HBc prevalence was 11.6%, with seropositivity increasing with age. Only one subject tested positive for HBsAg (0.2%). Approximately 67.4% (290/430) of the study population was susceptible, 20.9% (90/430) was vaccinated, 9.1% (39/430) had naturally acquired immunity, and 0.2% (1/430) had an acute infection. Older age and foreign nationality were identified as risk factors in both multivariate logistic regression models. The comparison highlights a reduction in the circulation of HBV infection markers (anti-HBc and HBsAg) over 30 years in Tuscany, particularly in younger age groups. Our seroprevalence study demonstrated a good level of protection against hepatitis B, primarily among individuals under 40 years old, the target group of the vaccination strategy.