Effective communication about science is a core skill undergraduates should learn, but little research has explored how students communicate about culturally controversial science topics. In this study, we explored how Black undergraduate science students took on the role of science communicators in their communities during the COVID-19 pandemic. We interviewed 23 Black students about their experiences learning about COVID-19 vaccines and communicating about COVID-19 vaccines to their communities. We found that students' racial/ethnic and science backgrounds made them feel a responsibility to be effective communicators about COVID-19 vaccines as potential trusted messengers within their communities. However, students were using limited strategies when communicating and were unsure how to communicate about COVID-19 topics effectively to those who were vaccine-hesitant or doubted the severity of the pandemic. Finally, students described ways that their biology instructors could have helped them be more confident when communicating about COVID-19 vaccines with their communities. Findings suggest that biology instructors could teach science communication principles in addition to content knowledge about culturally controversial science topics in their undergraduate classes to build on students' developing science communication skills.