Prevalence of hepatitis B surface antibodies and hepatitis B exposure in Belgium: results from a nationwide population-based serosurvey.

BACKGROUND: The WHO aims to eliminate hepatitis B virus (HBV) as a public health problem by 2030. HBV vaccination has reduced HBV incidence and mortality and is a cornerstone of the WHO elimination strategy. Belgium introduced universal infant HBV vaccination in 1999, with temporary catch-up vaccination for 12-year-olds, thereby covering all individuals born since 1987. This nationwide serosurvey assessed vaccine-induced hepatitis B surface antibody (anti-HBs) prevalence and natural HBV exposure in Belgium in 2020. METHODS: We analyzed 4955 left-over samples from SARS-CoV-2 sero-epidemiology studies in 2020. Samples from ambulatory patients outside lockdown periods were tested for anti-HBs and hepatitis B core antibodies (anti-HBc) to evaluate vaccine-induced vs. natural exposure-derived anti-HBs responses. Samples were stratified by region, 10-year age band, and sex, and were weighted to reflect the Belgian population. RESULTS: Overall, 47.3% (95%CI 45.6%-48.9%) of the Belgian population had anti-HBs ≥ 2 IU/L and was anti-HBc negative. Furthermore, 33.9% (95%CI 32.4%-35.5%) fulfilled the WHO-recommended threshold of anti-HBs ≥ 10 IU/L. Anti-HBc prevalence, indicating prior or current infection, was 3.8% (95%CI 3.2%-4.5%). Individuals born since 1987, thus eligible for universal vaccination, had higher anti-HBs (≥ 2 IU/L) and lower anti-HBc prevalences than those born before 1987 (71.6% vs. 31.4%, p < 0.001 and 0.8% vs. 5.9%, p < 0.001). Regional differences were observed with the lowest anti-HBc-/anti-HBs+ (≥ 2 IU/L) prevalence in Wallonia, and highest anti-HBc prevalence in the Brussels federal region. In weighted multivariate analysis, older age (aOR 0.96, 95%CI 0.96–0.97) and residency in Wallonia (aOR 0.80, 95%CI 0.69–0.93) were associated with lower anti-HBc-/anti-HBs+ (≥ 2 IU/L) positivity, while older age (aOR 1.03, 95%CI 1.03–1.04) and residency in Brussels (aOR 2.79, 95%CI 1.70–4.57), were associated with higher anti-HBc positivity. CONCLUSIONS: Belgium has achieved high levels of vaccine-induced protection, especially in cohorts born after the implementation of universal HBV vaccination. However, regional differences remain, highlighting the need for targeted efforts to improve coverage and reduce HBV exposure.