title: Influenza vaccine effectiveness in preventing inpatient and outpatient cases in a season dominated by vaccine-matched influenza B virus.
abstract: Studies that have evaluated the influenza vaccine effectiveness (VE) to prevent laboratory-confirmed influenza B cases are uncommon, and few have analyzed the effect in preventing hospitalized cases. We have evaluated the influenza VE in preventing outpatient and hospitalized cases with laboratory-confirmed influenza in the 2012-2013 season, which was dominated by a vaccine-matched influenza B virus. In the population covered by the Navarra Health Service, all hospitalized patients with influenza-like illness (ILI) and all ILI patients attended by a sentinel network of general practitioners were swabbed for influenza testing, and all were included in a test-negative case-control analysis. VE was calculated as (1-odds ratio) × 100. Among 744 patients tested, 382 (51%) were positive for influenza virus: 70% for influenza B, 24% for A(H1N1)pdm09, and 5% for A(H3N2). The overall estimate of VE in preventing laboratory-confirmed influenza was 63% (95% confidence interval (CI): 34 to 79), 55% (1 to 80) in outpatients and 74% (33 to 90) in hospitalized patients. The VE was 70% (41 to 85) against influenza B and 43% (-45 to 78) against influenza A. The VE against virus B was 87% (52 to 96) in hospitalized patients and 56% in outpatients (-5 to 81). Adjusted comparison of vaccination status between inpatient and outpatient cases with influenza B did not show statistically significant differences (odds ratio: 1.13; p = 0.878). These results suggest a high protective effect of the vaccine in the 2012-2013 season, with no differences found for the effect between outpatient and hospitalized cases.
authors.affiliation: a Instituto de Salud Pública de Navarra ; Pamplona , Spain.
authors.forename: Iván
authors.initials: I
authors.lastname: Martínez-Baz
authors.forename: Ana
authors.initials: A
authors.lastname: Navascués
authors.forename: Francisco
authors.initials: F
authors.lastname: Pozo
authors.forename: Judith
authors.initials: J
authors.lastname: Chamorro
authors.forename: Esther
authors.initials: E
authors.lastname: Albeniz
authors.forename: Itziar
authors.initials: I
authors.lastname: Casado
authors.forename: Gabriel
authors.initials: G
authors.lastname: Reina
authors.forename: Manuel García
authors.initials: MG
authors.lastname: Cenoz
authors.forename: Carmen
authors.initials: C
authors.lastname: Ezpeleta
authors.forename: Jesús
authors.initials: J
authors.lastname: Castilla
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D057286:Electronic Health Records; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology; D009981:Influenza B virus / Q000276:immunology / Q000472:pathogenicity; D007252:Influenza Vaccines / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control* / Q000821:virology*; D007297:Inpatients; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D010045:Outpatients; D012621:Seasons; D018571:Sentinel Surveillance; D013030:Spain / Q000453:epidemiology; D013997:Time Factors; D064166:Vaccine Potency; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: CI, confidence interval; ILI, influenza-like illness; OR, odds ratio; RT-PCR, reverse transcription polymerase chain reaction; VE, vaccine effectiveness; case-control study; effectiveness; influenza; influenza B virus; influenza vaccine; sentinel surveillance