*Abstract:* Psychological stress and chronic illnesses are associated with low levels of peripheral inflammation, which is thought to influence neural and behavioral function. Most experimental models however, elicit high concentrations of cytokines. The influenza vaccine has shown promise as a mild inflammatory challenge, but the timing of the acute immune response is unknown. This purpose of this study was to identify the timing of peak inflammation and explore psychological predictors of the immune response to vaccination. A sample of 21 healthy, young adults received the standard dose influenza vaccine and completed measures of depression, anxiety, sleep quality, and adverse childhood events. Blood samples were collected to measure concentrations of interleukin-6 (IL-6) in plasma 30 minutes prior to and 24, 48, and 72 hours post-vaccination. IL-6 peaked at 24 hours, returned to baseline levels by 48 hours, and remained low at 72 hours. Significant predictors of IL-6 change included higher anxiety levels and worse sleep quality. These findings have both methodological and conceptual implications for studying the effects of peripheral inflammation on the brain and behavior.