Introduction Social interaction is key in educational success. In online education, the creation of social interaction may be a challenge. This observational study evaluated to what extent social interactions occur during small private online courses (SPOCs). Methods Discussion forums of four courses of the UMC Utrecht's international Master's Program Epidemiology were assessed and posts were categorized as either content specific, functional/technical, or social. Results SPOCs at University Medical Center Utrecht showed substantial social interaction, creating involvement and student coherence, combined with students discussing and explaining content to each other. Interactions play a major role in SPOCs. Our results show that 43% of all discussion posts were social; 90% of social posts were initiated by students; and 94% was aimed at students. Conclusion SPOCs appear to provide a sustainable answer to the increased demand for online higher education, with an environment suitable for students to learn, in agreement with the need for social interaction in higher education.