Background/Objectives: Individuals with alcohol use disorder (AUD) and tobacco use disorder (TUD) are at increased risk for severe COVID-19 outcomes. However, real-world evidence on vaccine effectiveness (VE) in these populations remains limited, particularly in low- and middle-income countries. This study aimed to evaluate the effectiveness of three or more COVID-19 vaccine doses against mortality in hospitalized patients with AUD and TUD in Brazil. Methods: This retrospective cohort study used data from the SIVEP Gripe database, a national surveillance system of hospitalized COVID-19 cases in Brazil. The study included adults aged ≥18 years with confirmed SARS-CoV 2 infection between February 2020 and June 2025. The intervention was defined as receipt of three or more vaccine doses (fully vaccinated) versus no doses (unvaccinated). Propensity score matching was performed separately for AUD and TUD cohorts. Vaccine effectiveness was estimated using McNemar’s test for paired samples, and the average treatment effect (ATE) and number needed to vaccinate (NNV) were calculated. Results: Among 2,184,723 hospitalized patients, 12,115 had AUD and 45,679 had TUD. After matching, VE against mortality was 42% (95% CI: 27.5–53.5) in the AUD group and 52.6% (95% CI: 46.5–58.1) in the TUD group, compared to 58.5% and 58.9% in their respective non-exposed counterparts. The ATE was consistent across groups (approximately −0.12), and the NNV to prevent one death was 8 (95% CI: 6–15 for AUD; 7–12 for TUD). Conclusions: Although VE was attenuated in individuals with AUD and TUD compared to the general population, the absolute benefit of vaccination remained substantial.
Oliveira et al. (Thu,) studied this question.