Publication date: Jul 02, 2025

It is a public health priority to assess vaccine impact in marginalized populations disproportionately affected by COVID-19 to inform population-specific policies and reduce health disparities. We assessed COVID-19 vaccine uptake and effectiveness among people who inject drugs (PWID) in British Columbia, Canada. We used a population-based, linked data platform and a validated algorithm with high specificity to create a cohort of people aged 18-65 years with recent history of injection drug use (PWID). Vaccine uptake was assessed from Dec 15, 2020 (vaccine rollout) to the end of 2022. mRNA vaccine effectiveness against infection and severe outcomes was estimated using the test-negative study design during a period of Delta emergence/predominance (May 30th, 2021 to Nov 27th, 2021). We matched non-PWID to PWID on sociodemographics to create a comparison group. The cohort included 26,581 PWID, of whom a subset (1188 test-positive cases, 169 severe outcomes) were included in vaccine effectiveness analyses. By the end of 2022, the percentage of PWID vs. non-PWID who had received a vaccine dose was 72. 6 % vs. 83. 0 % (1st dose) and 64. 7 % vs. 81. 1 % (2nd dose). Vaccine effectiveness within 7-179 days after 2nd dose among PWID was 80. 0 % (95 % CI 76. 1-83. 3 %) against infection and 92. 9 % (95 % CI 88. 2-95. 7 %) against severe outcomes. Equivalent estimates for non-PWID were 90. 0 % (95 %CI 89. 3-90. 7 %) and 98. 7 % (95 %CI 98. 1-99. 2 %). Vaccine uptake and effectiveness were substantial among people with recent history of injection drug use, but somewhat lower relative to non-PWID matched on sociodemographic characteristics. While results suggest vaccines likely played a large role in reducing the population-level impact of COVID-19 among PWID, our results also highlight a potentially avoidable excess disease burden. Results should be interpreted within the context of the pervasive marginalization of people who use drugs. Findings may also have implications for vaccine outreach efforts and booster dose prioritisation.

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