Elderly Influenza Vaccine Immunogenicity Substudy

The body's immune system (fights infection) is known to decline during the aging process, resulting in an increased risk of catching infections. Vaccinations also are not as effective in protecting older people against infection as they are in younger people. The purpose of this study is to better understand how and why vaccines are not as effective in older people. The researchers believe that the immune response in older people who get a higher dose vaccine will be similar to the immune response in young adults who get the standard (lower) dose vaccine. This study is a substudy to a main study, evaluating flu vaccines in people 65 years and older. Volunteers who are in the main study will be asked if they will participate in the substudy. The substudy requires them to give 2 additional blood samples for an in-depth look at their immune response to the flu vaccine given in the main study. Substudy volunteers will have up to 3 clinic visits and participate up to 28 weeks.