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.