Development of Childhood Anti-Influenza Immunity

This study is a prospective surveillance of the immune response to seasonal vaccination in healthy children. The study will enroll a total of approximately 220 subjects. 140 children will be vaccinated with inactivated influenza vaccine (IIV) and will be divided into 4 age cohorts: 20 children between 6-12 months of age, 60 children greater than 12 months of age and born after 2009, 30 children with a birth date between 2006 and 2009, and 30 children with a birth date between 2003 and 2006. 80 children presenting with natural influenza infection prior to receipt of influenza vaccination also will be divided into 4 age cohorts: 20 children between 3-12 months of age, 20 children greater than 12 months of age with a birth date after 2009, 20 children with a birth date between 2006 and 2009, and 20 children with a birth date between 2003 and 2006. Influenza vaccines will be administered using age-appropriate guidelines in all years of the study: Fluzone 0.25 mL administered intramuscularly to children between 6 and 35 months of age and 0.5 mL to children 36 months of age and older. Subjects will be seen at one domestic site and their participation duration is 2 influenza seasons plus 1 optional season. The primary hypothesis being tested in this study is that there will be differences in the specificity, magnitude and functionality of CD4 T cell and B cell reactivity in a cohort of children depending on early childhood exposures. The primary objective of this study is to evaluate the relationship between influenza virus exposure, infection and vaccine history, and CD4 T cell reactivity in a cohort of children with well documented influenza exposures.