Abstract Introduction The COVID-19 outbreak disproportionally affects vulnerable populations including people who inject drugs (PWID). Social distancing and stay-at-home orders might result in a lack of access to medical and social services, poorer mental health, and financial precariousness, and thus, increases in HIV and HCV risk behaviors. This article explores how the HIV/HCV risk behaviors of PWID in Haiphong, a city with high harm reduction service coverage in Vietnam, changed during the early phase of the COVID-19 pandemic, and what shaped such changes, using the risk environment framework. Method We conducted three focus group discussions with peer outreach workers in May 2020 at the very end of the first lockdown, and 30 in-depth interviews with PWID between September and October 2020, after the second wave of infection in Vietnam. Discussions and interviews centered on the impact of the COVID-19 pandemic on their lives, and how their drug use and sexual behaviors changed as a result of the pandemic. Results The national shutdown of nonessential businesses due to the COVID-19 epidemic caused substantial economic challenges to participants, who mostly were in a precarious financial situation before the start of the epidemic. Unsafe injection is no longer an issue among our sample of PWID in Haiphong thanks to a combination of different factors, including high awareness of injection-related HIV/HCV risk and the availability of methadone treatment. However, group methamphetamine use as a means to cope with the boredom and stress related to COVID-19 was common during the lockdown. Sharing of smoking equipment was a standard practice. Female sex workers, especially those who were active heroin users, suffered most from COVID-related financial pressure and may have engaged in unsafe sex. Conclusion While unsafe drug injection might no longer be an issue, group methamphetamine use and unsafe sex were the two most worrisome HIV/HCV risk behaviors of PWID in Haiphong during the social distancing and lockdown periods. These elevated risks could continue beyond the enforced lockdown periods, given PWID in general, and PWID who are also sex workers in particular, have been disproportionately affected during the global crisis.