These models present as two of many models constituting causal knowledge base established via the COVID-I project. Please find the COVID-I Project Overview [here][1]. Respiratory system: The respiratory causal DAG describes the physiological process underlying COVID-19 in the respiratory system, outlining multiple and often concurrent pathways from the initial replication of the virus to key downstream complications such as multi-organ failure. The three major pathways depicted in this model are mechanical pathway, gas exchange pathway, and coagulation pathway. This model was included in our [paper][2] published in BMC Medical Research Methodology and a [causal BN][3] based on the causal DAG (i.e., the DAG combined with a parameterisation) is provided for public access through this repository. Complications: The complications causal DAG describes the main physiological processes underlying the progression of COVID-19 from the initial infection in the respiratory system to complications in other organs. The model explicitly describes the status (dysfunction) of nine key organ systems, namely, respiratory, vascular, cardiac, liver, kidney, hematologic, gastrointestinal, cortical and brainstem dysfunctions. Among these, we choose to paint a more fine-grained picture of the vascular and cardiac systems due to their potential earlier involvement, as well as more significant system-wide impact on other organs. This model was included in our paper published in BMC Medical Research Methodology and a [causal BN][4] based on the causal DAG (i.e., the DAG combined with a parameterisation) is provided for public access through this repository. [1]: https://osf.io/bynr6/wiki/COVID-I%20Project%20Overview/?view_only=afbdfb3e22c2406cad1ae142a3e5a3b2 [2]: https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/s12874-023-01856-1 [3]: https://osf.io/zydbx?view_only=afbdfb3e22c2406cad1ae142a3e5a3b2 [4]: https://osf.io/3rz5h?view_only=afbdfb3e22c2406cad1ae142a3e5a3b2