During the COVID-19 outbreak the transdisciplinary research project CAVE (Community Engagement and Vulnerability Assessment in Epidemics) investigated perceptions and practicability of public health communication among stakeholders of care and social facilities in Austria. It aimed at finding accurate definitions of vulnerability in the context of epidemics and at developing operational models for engagement of vulnerable groups in co-creating epidemic response mechanisms. Transdisciplinary methods included semi-structured interviews, focus group discussions, and desk reviews as well as spatial analysis and composite indicator-based mapping methods. Informants and participants in the community engagement phase represented clients as well as middle and lower management levels of Austrian care and social facilities for older persons and persons with cognitive impairments, persons depending on mobile healthcare services, homeless people, and socially deprived communities. A narrow definition of vulnerability as well as missing strategies for participation and community engagement limited communication with stakeholders and the implementation of protective measures. An inclusive definition of vulnerability beyond medical and physical indicators should be employed to account for social, psychological, and emotional aspects contributing to a higher risk of being affected by epidemics. The CAVE model provides a multi-level definition of vulnerability that allows for participatory engagement in co-creating adapted crisis response measures. We suggest policymakers and health authorities to consider a broader definition of vulnerability and to commit to pro-active engagement with stakeholders representing these sectors. This requires the establishment and maintenance of communication structures as well as political recognition of civic participation in the creation and implementation of epidemic response measures.