The immune response in patients with Coronavirus Disease 2019 (COVID-19) is highly variable and is linked to disease severity and mortality. However, antibody and cytokine responses in the early disease stage and their association with disease course and outcome are still not completely understood. In this large, multi-centre cohort study, blood samples of 434 Belgian COVID-19 hospitalized patients with different disease severities (ranging from asymptomatic/mild to critically ill) from the first wave of the COVID-19 pandemic were obtained. Baseline antibody and cytokine responses were characterized and associations with several clinical outcome parameters were determined. Anti-spike immunoglobulin (Ig)G and IgM levels were elevated in patients with a more severe disease course. This increased baseline antibody response however was associated with decreased odds for hospital mortality. Levels of the pro-inflammatory cytokines IL-6, IP-10 and IL-8, the anti-inflammatory cytokine IL-10 and the antiviral cytokines IFN-α, IFN-β and IFN-λ1 were increased with disease severity. Remarkably, we found significantly lower levels of IFN-λ2,3 in critically ill patients compared to patients of the moderate and severe disease category. Finally, levels of IL-8, IL-6, IP-10, IL-10, IFN-α, IFN-β, IFN-γ and IFN-λ1 at baseline were positively associated with mortality, whereas higher IFN-λ2,3 levels were negatively associated with mortality. ; The authors would like to thank Hilde Kelchtermans (Jessa Hospital, Hasselt, LCRC), Inge Thijs (Ziekenhuis Oost-Limburg, Genk, LCRC) and Helene Piccard (Hasselt University, LCRC) as research coordinators. We thank Koen Magerman (Jessa Hospital, Hasselt), Kimberly Vanhees (Jessa Hospital, Hasselt, University Biobank Limburg, Hasselt) and Kim Ulenaers (Hasselt University, Biomedical Research Institute and University Biobank Limburg, Hasselt), for sample collection and storage. We also thank Igna Rutten (Hasselt University, Biomedical Research Institute), Laura Dusaer (Hasselt University, ...