title: Duration of protection provided by live attenuated influenza vaccine in children.
abstract: BACKGROUND
  Reliable availability of influenza vaccine before October could enable the vaccination of many children who might not otherwise be vaccinated.
  
  
  METHODS
  Available data for children were analyzed to describe protection provided by live attenuated influenza vaccine (LAIV) for greater than 5 months postvaccination.
  
  
  RESULTS
  Four studies conducted in children aged 6 months to 18 years were identified. Culture-confirmed efficacy against A/H1N1 and A/H3N2 strains at 9-12 months postvaccination was 77% [95% confidence interval (CI): 53-89%] to 100% (95% CI: 68-100%) and through a second influenza season without revaccination was 56% (95% CI: 31-73%) and 57% (95% CI: 6-82%), respectively. Against B strains, 1 study demonstrated 86% (95% CI: 59-95%) efficacy at 5-7 months. Another study demonstrated 27% (95% CI: -62% to 67%) efficacy at 9-12 months compared with 74% (95% CI: 39-89%) at 1 to <5 months during a period of antigenic drift for circulating B strains. A third study estimated 50% (95% CI: -49% to 83%) efficacy against influenza B strains through a second season without revaccination.
  
  
  CONCLUSIONS
  In children, live attenuated influenza vaccine provided sustained protection against influenza illness caused by antigenically similar strains. Efficacy at 1 to <5 months postvaccination was comparable to that at 9-12 months for A/H1N1 and A/H3N2 strains and at 5-7 months for B strains. Meaningful efficacy was seen through a second season without revaccination, although at a lower level than during the first 12 months postvaccination.
authors.affiliation: MedImmune, One MedImmune Way, Gaithersburg, MD 20878, USA. ambrosec@medimmune.com
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Ambrose
authors.forename: Tingting
authors.initials: T
authors.lastname: Yi
authors.forename: Robert E
authors.initials: RE
authors.lastname: Walker
authors.forename: Edward M
authors.initials: EM
authors.lastname: Connor
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D004311:Double-Blind Method; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000187:drug effects; D053122:Influenza A Virus, H3N2 Subtype / Q000187:drug effects; D009980:Influenza A virus / Q000145:classification* / Q000187:drug effects*; D009981:Influenza B virus / Q000187:drug effects*; D007252:Influenza Vaccines / Q000008:administration & dosage*; D007251:Influenza, Human / Q000276:immunology / Q000517:prevention & control* / Q000821:virology; D016032:Randomized Controlled Trials as Topic; D013997:Time Factors; D016896:Treatment Outcome; D014611:Vaccination
chemical_list: D007252:Influenza Vaccines