Attendance in the first lecture is mandatory for the participation in the course. If an absence cannot be avoided inform the lecturer before class and provide some form of proof for the absence (e.g. medical confirmation) in the next session. In total, a minimum requirement for attendance of 80% is required to pass the course.
If the attendance falls below 80% for students receiving partial credit, students are graded with 5 (Nicht genügend). See further: https://www.wu.ac.at/fileadmin/wu/h/students/Pruefungsorganisation/Gesetzesgrundlagen/Pruefungsordnung_03.12.2014.pdf