Toups MS, et al. - Researchers presumed that patients with depression and anxiety should have a more pronounced change in affect after receiving a mild immune stimulus. This hypothesis was based on the theory that depression is physiologically related to sickness. In this study, the validity of this notion was tested and, it was found that patients with depression and/or anxiety vs mentally healthy individuals had a greater impact of influenza vaccine on their mood. This finding lends support to the proposed link between depression and sickness behavior.