Abstract
BACKGROUND: Vaccine hesitancy is increasingly recognized as a health challenge affecting populations worldwide. Given the biological vulnerabilities and structural barriers people who use substances and/or have behavioral addictions face, this systematic review aims to evaluate whether this subpopulation is less prone to adhere to vaccination recommendations. METHODS: Electronic searches of published original research were conducted in PubMed, EMBASE, Scopus, and PsycINFO from database inception to December 2022. Our strategy encompassed retrievals regardless of languages and date of publication. Animal studies, abstracts without a full manuscript, and studies which were considered to have lower robustness of scientific evidence were excluded. Outcomes measured were vaccine acceptance, uptake, and adherence. Results were interpreted through a narrative synthesis. RESULTS: The search yielded 103 retrievals encompassing data collected on 5 576 374 persons who were predominantly residents of Europe (n = 39) and North America (n = 27). Tobacco use, the substance for which many studies were found (n = 91), was significantly associated with poorer vaccine acceptance, uptake and adherence for influenza, COVID-19, human papillomavirus (HPV), and maternal and childhood vaccines. Peri-natal and parental substance use was identified as a risk factor for suboptimal vaccine-related outcomes concerning maternal COVID-19 and childhood vaccines. Finally, people identified as 'using', 'abusing', or 'misusing' drugs or substances may be at decreased odds of all outcomes in various vaccines. CONCLUSIONS: Collectively, the studies identified several groups with statistically significant greater vaccine hesitancy and decreased engagement among whom targeted measures could be beneficial. Timely evidence, especially on behavioral addictions and substances besides tobacco, is lacking, and warrants urgent attention.