Comparison of Full-dose Flu Vaccine to Half-dose Flu Vaccine

Inclusion Criteria: * Able to understand and comply with all study procedures including availability for all study visits and follow up surveys within 6 months following study enrollment. * DEERS eligible beneficiaries eligible for influenza vaccination and able to give informed consent. * Age 18-49 * Patients presenting to travel clinic with no exclusion criteria; * Household contacts and out-of-home caretakers of infants from 6-23 months of age; * Hospital and/or employees providing service to the public who are not eligible for the post-October 5th recommendations for priority immunization; * DOD employees eligible for influenza vaccination prior to October 5th but excluded in the post October 5th guidelines; * People living in dormitories or under other crowded conditions, to prevent outbreaks; * Ages 50-64 years of age who are not eligible for the post-October 5th recommendations for priority immunization and with no standard of care contraindications to vaccination. * Eligible in the Department of Defense for influenza vaccination Exclusion Criteria: * all children aged \< 18 years (includes children aged 6 months-18 years on chronic aspirin therapy); * adults aged \>65 years; * persons aged 2-64 years with underlying chronic medical conditions: * includes persons with chronic cardiac or pulmonary disease, diabetes mellitus, hemoglobinopathy, or immunosuppressive illness; * any acute or chronic condition that, in the opinion of the investigator, would render vaccination unsafe or interfere with the evaluation of response. * use of experimental vaccines or medications within 30 days of study entry; * receipt of parenteral immunoglobulin within 60 days of study entry; * all women who will be pregnant during the influenza season; * residents of nursing homes and long-term care facilities; * health-care workers involved in direct patient care and included in DOD priority 1; and; * military recruits; * out-of-home caregivers and household contacts of children aged \<6 months. * Anyone with clinical contraindications for receiving the inactivated influenza vaccine such as a history of severe allergic reaction to prior influenza vaccinations, severe allergy to egg and/or egg proteins and gelatin. * DOD Priority 1: Deployed or deploying (with orders) service members and others designated as critical to national defense. * DOD Priority 2: Medically high risk in accordance with ACIP guidelines (includes health-care workers with direct patient contact) * Any acute or chronic condition that, in the opinion of the investigator or her provider designee would render vaccination unsafe or interfere with the evaluation of the response.