Regional distribution of serological evidence of vaccine-induced immunity to hepatitis B among cancer patients in a city in southeastern Brazil.

Vaccination is the primary strategy for preventing hepatitis B virus (HBV) infection, but its frequency remains insufficiently characterized among cancer patients. This study evaluated the regional distribution of serological evidence compatible with vaccine-induced immunity to hepatitis B among cancer patients residing in Sao Paulo city, Brazil. We conducted a retrospective observational study of adult patients who underwent hepatitis B surface antibody (anti-HBs) serological testing at the Instituto do Cancer do Estado de Sao Paulo (ICESP) in 2023. Serological evidence compatible with vaccine-induced immunity was defined as reactive anti-HBs and non-reactive hepatitis B core antibody (anti-HBc). Univariable and multivariable Poisson regression analyses were performed to identify associated factors. Among 1,143 patients, the mean age was 57.4 ± 16.42 years, 61.9% were female, 60.6% self-identified White, and 76.8% had solid tumors. Overall, 26.2% of cancer patients had serological evidence compatible with vaccine-induced immunity to hepatitis B. Descriptively, the North Zone had a lower frequency than the South Zone (20.7% versus 28.9%), although regional differences were not statistically significant after multivariable adjustment. Female sex (adjusted prevalence ratio [aPR] = 1.67, 95% CI: 1.23-2.27, p = 0.001) and younger age (18-39 years versus ≥ 60 years: aPR = 6.89, 95% CI: 4.72-10.95, p < 0.001) were independently associated with serological evidence compatible with vaccine-induced immunity. These findings indicate a low frequency of serological evidence compatible with vaccine-induced immunity to hepatitis B among cancer patients across Sao Paulo, particularly among older adults and men.