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. 2015;11(7):1626-33.
doi: 10.1080/21645515.2015.1038002.

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

Iván Martínez-Baz  1 , Ana Navascués, Francisco Pozo, Judith Chamorro, Esther Albeniz, Itziar Casado, Gabriel Reina, Manuel García Cenoz, Carmen Ezpeleta, Jesús Castilla; Primary Health Care Sentinel Network and Network for Influenza Surveillance in Hospitals of Navarra
Collaborators, Affiliations

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

Iván Martínez-Baz et al. Hum Vaccin Immunother. 2015.

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.

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.

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Figures

Figure 1.
Figure 1.
Number of influenza cases and test-negative controls, and incidence of influenza-like illness by week, 2012–2013 season in Navarra, Spain.
See this image and copyright information in PMC

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