Characterization of the Innate Immune Response in Healthy NIH Employees at Baseline and After Immunization With the H1N1 Vaccine

Background: * The Center for Human Immunology, Autoimmunity, and Inflammatory Diseases is conducting research investigating how the swine flu (H1N1) vaccine affects the immune system. The exposure to the new swine flu vaccine gives us a rare opportunity to learn about how the human immune system responds to a new vaccine. * Researchers are interested in collecting blood samples from individuals who have received the vaccine. Participants will be selected from a group of healthy volunteers who will be receiving the H1N1 vaccine because it is mandatory for their work at the National Institutes of Health. This protocol will be one of the first studies to characterize the human innate immune response to H1N1 vaccine. Objectives: \- To collect blood samples for research purposes before and after participants receive a standard non-research vaccination against swine flu (H1N1). Eligibility: * Healthy individuals 18 years of age and older who are employees of the National Institutes of Health. * Individuals who have had confirmed cases of influenza in the past year are not eligible to participate. Design: * Participants will be admitted for a 36-hour inpatient stay, during which blood samples will be taken frequently. Participants will have a standard intravenous catheter (similar to the one used for intravenous infusions) put in place to avoid multiple needle sticks. * Participants will be assigned into one of two groups; the two groups differ in the timing of blood draws but not in the overall amount of blood drawn. * Group 1: Blood samples 30 minutes before and immediately before vaccination. Additional samples will be taken 2, 4, 6, 8, 10, 12, 14, 16, 18, 24, 30, and 36 hours after vaccination. * Group 2: Blood samples 30 minutes before and immediately before vaccination. Additional samples will be taken over the following 36 hours, with exact timing to be determined based on the findings from group 1. * All participants will provide blood samples 7 days after b