Vaccination is a leading public health intervention for reducing morbidity and mortality from influenza worldwide. Vaccine optimization is hampered by lack of understanding the natural history of infection and immunity, including the full complement of maternal immunity imparted to infants. This gap in understanding can be addressed only through a well-designed birth cohort study. Up to 1500 mother-infant pairs will be enrolled at or after week 34 in pregnancy over three flu seasons, up to four years of age depending on birth month, at two sites. Follow-up will occur from the third trimester until the child is three to four years of age, along with medical records review to ascertain outcomes not captured through weekly illness and respiratory surveillance, and medical record review up to 18 years of age. The primary aim is to rigorously document the natural history of infection and immune response to influenza in study infants for at least three entire flu seasons.
