The COVID-19 pandemic has drawn much attention from the public in 2020. Since restrictions related to COVID-19 took place, troubling news about an increase in overdose-related fatalities emerged. In fact, 2021 saw a record high number of overdose death. Because those who are already subject to the negative effects of social and economic determinants of health (e.g., older persons, racial/ethnic minorities) are also affected by both COVID-19 and fatal overdose disproportionately, this collision between the COVID-19 pandemic and the overdose epidemic is creating a syndemic. Because the pandemic has been associated with an increase in substance use for racial/ethnic minorities, existing health disparities are expected to exacerbate. A clear example is the City of Detroit, where 90% of the residents are racial/ethnic minorities. As of May 2022, Detroit’s COVID-19 mortality rate is 522 per 100k residents, and its fatal overdose rate is 77 per 100k, each two to three times higher than the national average, while the COVID-19 confirmation rate is lower. Another concerning observation is Detroit’s vaccination rate of 41.4%, which is lower by over 20 % point than the national average. This syndemic, combined with low vaccination rates, is likely to produce negative impacts beyond health, including the economy through the lost opportunity costs. Despite this concerning trend, little is known about the effect of the syndemic on communities of persons who inject drugs (PWID), including basic statistics about COVID-19 vaccination and harm reduction practices. The mechanisms behind these preventive practices are complicated, involving not only PWID’s own behaviors but also influences from their social networks. Moreover, the mechanism may differ by age and race/ethnicity. Therefore, it is critical to examine the syndemic with social networks, particularly for older and racial/ethnic minority PWID who are at a greater risk. This diversity supplement study builds on a parent R01 grant that currently is in the field collecting data from PWID using respondent driven sampling (RDS) in Southeast Michigan. Based on our prior work, a majority of PWID from this area are older and racial/ethnic minorities, implying robust statistical power for the analysis that provides insights into older PWID and racial/ethnic minority PWID. Thanks to the RDS method, innovative social network measures beyond ego-centric self-reports will be introduced in understanding PWID’s vaccination and harm reduction practices. The proposed research has strong potential to address the urgent need to assess the syndemic and its effect on older PWID. Specifically, the study aims to describe the extent of COVID-19 vaccination, overdose incidence and preventive practices among PWID and analyze them as a function of social networks with specific considerations given to age and race/ethnicity. This diversity supplement is uniquely positioned to provide a trainee-candidate, a doctoral student in survey...