Background: Increased depressive symptoms and anxiety symptoms have been observed in about 23% of all post-COVID patients, also called post-COVID depression (Huang et al., 2021). However, what a) promotes post-COVID depression after the disease and whether it is b) even post-Covid specific has not yet been conclusively understood and will be investigated in this proposed research. The theoretical basis of the proposed work is Cacioppo, Peplau, and Perlman's theory of loneliness, Bandura's self-efficacy theory, and Schwarzer's HAPA model.

Objectives: The aim of the study is to investigate possible predictors and factors that may be associated with the development and maintenance of mental and physical health constrains including depression and anxiety symptomatology as well as loneliness in hospitalized post-COVID patients and non-COVID patients in Germany. Furthermore, it will be investigated whether psychological interventions have an effect on anxiety and depression symptomatology, on loneliness values, self-efficacy and perceived social support values. Specifically, the research aim is to examine the relationships between loneliness, self-efficacy, and social support and to address the question of what factors increase the risk of post covid depression/anxiety, and to test the buffering effect of physical and social activities. For this purpose, a correlational study and an experimental group comparison will be applied, in which two interventions will be performed on post-COVID patients and non-COVID patients. These two data collections will serve as the basis for a later longitudinal study, which is still in the planning stage, as follow-up questions still need to be elaborated. Methods: Around 300 patients should be included in the study. The correlation study at the first measurement point also includes a regression analysis (moderated mediation analysis). Furthermore, an experimental group comparison is performed. For the first group, a psychological intervention for psychoeducational measures and psychosocial support, was designed according to the recommendations of the DGP - Deutsche Gesellschaft für Pneumologie und Beatmungsmedizin e.V. for the rehabilitation of COVID-19 patients (DGP, 2020). The second intervention was designed after Cacioppo's intervention EASE, for processing loneliness. In this experiment, the psychological interventions will be applied to both groups of patients (non-Covid/Covid patients). The interventions start approximately two days after data collection at T0. The second measurement time point (T1) is scheduled at the time of patient discharge after the interventions have been implemented. Only patients who scored 8 or higher on the Hospital Anxiety and Depression Scale (HADS) at admission will participate in the interventions. Patients will be asked to complete the questionnaire again six months after discharge to include a third measurement point and to conduct the aforementioned longitudinal study. Patients who refuse to participate in one of the interventions but nevertheless agree to complete the questionnaires at the measurement time points are treated according to the standards of the complex treatment in early rehabilitation in which a twice psychological contact and screening by means of HADS is obligatory. They form a third group. The following instruments will be used: Items from the UCLA Loneliness Scale (Russel, 1980, German version), the Hospital Anxiety and Depression Scale (Snaith \& Zigmond, 2010), Perceived Social Support Questionnaire (F-SozU K-6, Fydrich et al., 2009); SWE - General Self-Efficacy Expectancy Scale (Schwarzer et al., 1999); various self-efficacy instruments, such as staging and Activities Against Loneliness (Lippke, 2007, adapted from Godin \& Shepard, 1985). It is expected that self-efficacy and social support play a role as mediator variables and moderator variables and that the symptomatology of depression and anxiety improves after an intervention in COVID and non-COVID patients alike. The findings of this research will contribute to a better understanding of the experience and behavior of patients with and without an infection with COVID-19 in early rehabilitation and identify opportunities for psychological intervention.

The ethics committee of Jacobs University Bremen, where Prof. Dr. Lippke supervises the PhD project, has already approved the research project. Therefore, the project is already in the recruitment phase in order to be able to use data from the third wave from the first quarter of 2021, as this is a special situation in the pandemic and the data would not be reproducible in this way.