Impact of Repeated Influenza Immunization on Respiratory Illness in Children With Preexisting Medical Conditions

Annual influenza immunization in medical risk groups is recommended in many countries. Recent evidence suggests that repeated inactivated influenza vaccine (IIV) immunization throughout childhood may impair long-term immunity against influenza. We assessed whether prior immunization altered the effect of IIV in children with preexisting medical conditions on primary care–diagnosed respiratory illness (RI) episodes during the influenza season