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Pediatric Influenza Vaccine Effectiveness Study


The Pediatric Vaccine Effectiveness Study is a case-control study that examines the effectiveness of the trivalent influenza vaccine (flu shot) and the effectiveness of one dose versus two doses of the vaccine in eligible children. The study began during the 2005-06 influenza season and continued through the 2007-08 influenza season. In total, 40 cases and 160 conrols were enrolled over the three influenza seasons.

Goals & Objectives

  • To evaluate the overall effectiveness of trivalent inactivated influenza vaccine (TIV) among children during influenza seasons in preventing hospitalization with a laboratory-confirmed, community-acquired influenza virus infection.
  • To evaluate the effectiveness of 1 versus 2 doses of TIV in preventing an influenza-associated hospitalization among children.
  • To evaluate possible barriers to implementation of the Advisory Committee on Immunization Practices (ACIP) recommendations for annual influenza vaccination among children.


Vaccination with trivalent inactivated influenza vaccine (TIV) has been the major strategy for reducing the effect of influenza virus infections for many years. Influenza viruses are responsible for annual epidemics of respiratory disease that affect all segments of the U.S. population and result in considerable morbidity and mortality. Young children are at higher risk of influenza-associated complications and hospitalizations compared with healthy older children and adults aged <65 years. Children with chronic, underlying medical conditions such as asthma are at even greater risk than healthy children for influenza- associated complications. The recent implementation of influenza vaccination in young children based on recommendations from ACIP and AAP prompted us to evaluate the effectiveness of TIV in preventing hospitalization among children. This evaluation was conducted through the Respiratory Diseases Activity of the Emerging Infections Program Network of the Centers for Disease Control and Prevention, by building upon the existing surveillance system for laboratory-confirmed influenza in children.

Laboratory-confirmed influenza reports among New Haven County pediatric residents were received from the Connecticut Department of Public Health. These laboratory-confirmed cases were followed up by contacting hospital infection control practitioners (ICPs) to identify cases of pediatric influenza-related hospitalizations at the ICPs' respective hospitals. For each influenza-related hospitalized case enrolled, four comparison children who were not hospitalized with an influenza infection were recruited. These comparison children were identified using birth certificate data and were matched by zip code and age. Once consent from a parent or legal guardian was obtained, information was collected through interview and by contacting the child's health care provider. Health care providers were contacted for both cases and controls to obtain immunization and medical history. Children were considered immunized if there was any report of receipt of TIV from parent or medical records. All children were considered immunized for an influenza season if they received TIV since September 1 of that particular influenza season and at least 14 days prior to the date of hospital admission for the case.