Using the influenza vaccine as a mild, exogenous inflammatory challenge: When does inflammation peak?

BACKGROUND: The influenza vaccine has shown promise as a mild, exogenous inflammatory challenge, but use of this model is limited by lack of knowledge about the timing of the inflammatory response. This study was designed to characterize the time-course of the acute inflammatory response and explore psychological and behavioral predictors of that response. METHODS: Twenty-one young, healthy individuals were recruited to receive the annual influenza vaccine. Serial blood samples were collected immediately before, and 24, 48, and 72 ​h following influenza vaccination. Interleukin (IL)-6 concentrations were assayed at each time-point and psychological and behavioral factors (anxiety and depressive symptoms, sleep disturbance, and childhood adversity) were assessed at baseline. RESULTS: Significant elevations in IL-6 were observed at 24 ​h post-vaccination (mean increase ​= ​0.70 ​pg/mL, Cohen’s d ​= ​0.54, p ​= ​.018)), with 61.9% of participants exhibiting peak concentrations at that time point, χ(2) ​= ​22.54, p ​< ​.001, η ​= ​0.52. In exploratory analyses, sleep disturbance was associated with greater increases in IL-6 at 24 ​h. CONCLUSIONS: By identifying the peak IL-6 response to influenza vaccination among a sample of young, healthy individuals, these findings support the use of the influenza vaccine in future PNI research. This vaccine model can be used to examine the impact of mild inflammatory challenges on the brain and behavior, and to identify psychological and behavioral factors (e.g., anxiety, sleep) that modulate inflammatory reactivity.