The process of developing a behavior change intervention can cover a long time period. However, in times of need, this development process has to be more efficient and without losing the scientific rigor. In this article, we describe the just-in-time, planned development of an online intervention in the field of higher education, promoting COVID-19 vaccination among university students, just before they were eligible for being vaccinated. We demonstrate how intervention development can happen fast but with sufficient empirical and theoretical support. In the developmental process, Intervention Mapping (IM) helped with decision-making in every step. We learned that the whole process is primarily depending on the trust of those in charge in the quality of the program developers. Moreover, it is about applying theory, not about theory-testing. As there was no COVID-19-related evidence available, evidence from related fields helped as did theoretical knowledge about change processes, next to having easy access to the target population and important stakeholders for informed qualitative and quantitative research. This project was executed under unavoidable time pressure. IM helped us with systematically developing an intervention, just-in-time to positively affect vaccine acceptance among university students.
Keywords: COVID-19 vaccination; Intervention Mapping; health promotion; intervention development; time lags.