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.
Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed.
Funding
This work was supported by the Carlos III Institute of Health (PS12/00087), the Spanish Ministry of Health (EC11–302), and by the I-MOVE program of the European Center for Disease Prevention and Control (ECDC).
Note
Members of the Primary Health Care Sentinel Network of Navarra: I Abad, P Aldaz, E Álvarez, JJ Arana, I Arceiz, E Arina, I Arribas, MD Artajo, A Arza, B Azagra, FC Bartolome, C Bernués, C Bolea, A Brugos, B Cano, MV Castresana, JC Cenoz, F Cia, B Compains, JR Corpas, F Cortés, B Churío, PC Cuevas, EM Da Costa, J Díez Espino, M Doiz, FJ Escribano, MJ Esparza, V Etayo, C Fernández Alfaro, B Flamarique, J Gamboa, ML Garcés, L García Blanco, AB German, A Giner, M Gómara, N Goñi, MJ Guillorme, JO Guiu, JC Gurbindo, MJ Guruchaga, JA Heras, MC Hijos, MS Indurain, B Iñigo, SE Juan Belloc, JJ Jurio, MP León, JJ Longás, JJ Miner, M Moreno, MA Moros, U Navarro, FJ Orozco, M Orte, P Palacio, J Palau, C Pérez Lecumberri, P Pérez Pascual, B Pérez Sanz, A Prado Virto, M Prado Santamaria, A Puig Arrastia, E Ridruejo, M Ramos, BE Rípodas, M Rodríguez, MA Roncal, I Ruiz Puertas, C Sánchez Vázquez, P Sarrasqueta, MA Senosiain, J Sola, M Sota, ME Ursua, IA Urtasun, MJ Vigata, MT Virto, JM Vizcay.
Members of the Network for Influenza Surveillance in Hospitals of Navarra: P Artajo, X Beristain, E Bernaola, J Chamorro, M Esquiroz, P Fanlo, F Gil, M Gabari, J Hueto, C Martín, L Peña, C Pérez, M Ruiz (Complejo Hospitalario de Navarra), M Fernández-Alonso, J Núñez (Clínica Universidad de Navarra), JJ García Irure, M Torres, MT Ortega (Hospital Reina Sofía, Tudela), F Lameiro, L Barrado (Hospital García Orcoyen, Estella), N Alvarez (Servico Navarro de Salud), M Guevara, F Irisarri, M Arriazu, A Zabala, A Barricarte, J Castilla (Instituto de Salud Pública de Navarra).