Influenza vaccine effectiveness in preventing inpatient and outpatient cases in a season dominated by vaccine-matched influenza B virus

• Published in: Human vaccines & immunotherapeutics Vol. 11; no. 7; pp. 1626 - 1633
• Main Authors: Martínez-Baz, Iván, Navascués, Ana, Pozo, Francisco, Chamorro, Judith, Albeniz, Esther, Casado, Itziar, Reina, Gabriel, García Cenoz, Manuel, Ezpeleta, Carmen, Castilla, Jesús
• Format: Journal Article
• Language: English
• Published: United States Taylor & Francis 03.07.2015
• Subjects: Adolescent; Adult; Aged; Case-Control Studies; case-control study; Child; Child, Preschool; CI, confidence interval; effectiveness; Electronic Health Records; Female; Humans; ILI, influenza-like illness; influenza; Influenza A Virus, H1N1 Subtype - immunology; Influenza A Virus, H3N2 Subtype - immunology; influenza B virus; Influenza B virus - immunology; Influenza B virus - pathogenicity; influenza vaccine; Influenza Vaccines - immunology; Influenza, Human - epidemiology; Influenza, Human - prevention & control; Influenza, Human - virology; Inpatients; Male; Middle Aged; Odds Ratio; OR, odds ratio; Outpatients; Research Paper; RT-PCR, reverse transcription polymerase chain reaction; Seasons; Sentinel Surveillance; Spain - epidemiology; Time Factors; Vaccine Potency; VE, vaccine effectiveness; Young Adult; Spain; effectiveness; influenza; influenza vaccine; CI, confidence interval; ILI, influenza-like illness; case-control study; VE, vaccine effectiveness; influenza B virus; sentinel surveillance; OR, odds ratio; RT-PCR, reverse transcription polymerase chain reaction
• ISSN: 2164-5515; 2164-554X
• DOI: 10.1080/21645515.2015.1038002

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.