Vaccination coverage among people who inject drugs: A systematic review

Background: People who inject drugs may be at excess risk of acquiring vaccine-preventable diseases and negative associated health outcomes, but experience barriers to vaccination. We aimed to determine vaccination coverage among people who inject drugs globally. Methodology: We conducted systematic searches of the peer-reviewed and grey literature, date limited from January 2008 to August 2023, focusing on diseases for which people who inject drugs are at elevated risk for and for which an adult vaccination dose is recommended (COVID-19, hepatitis A, hepatitis B, human papillomavirus, influenza, pneumococcal disease, tetanus). To summarise available data, we conducted a narrative synthesis. Results: We included 78 studies/reports comprising 117 estimates of vaccination coverage across 36 countries. Most estimates were obtained from high income countries (80%, n=94). We located estimates for hepatitis B vaccination in 33 countries, which included 18 countries with data on serological evidence of vaccine-derived hepatitis B immunity (range: 6-53%) and 22 countries with self-report data for vaccine uptake (<1-96%). Data for other vaccines were scarcer: reported hepatitis A vaccination coverage ranged 3-89% (five countries), COVID-19 ranged 4-84% (five countries), while we located estimates from fewer than five countries for influenza, tetanus, pneumococcal disease, and human papillomavirus. Conclusion: Estimates were sparse but where available indicative of suboptimal vaccination coverage among people who inject drugs. Improving the consistency, timeliness, and geographic coverage of vaccine uptake data among this population is essential to inform efforts to increase uptake.