Healthy individuals seen at the Employee Health Clinic who will be eligible to receive influenza vaccine Willingness to comply with study expectations Subject or legal representative must understand the investigational nature of this study and sign an Independent Ethics Committee/Institutional Review Board approved written informed consent form prior to receiving any study related procedure INTERVENTION COMPONENT ONLY: Willing to suspend use of any other vitamin D supplementation during the 3 month treatment interval; if currently using > 2,000 IU/day of vitamin D supplementation, must suspend use 30 days prior to enrollment