Alin Gherasim1, Francisco Pozo2, Salvador de Mateo3, Inma Aspiritxaga Gamarra4, Manuel García-Cenoz5, Tomas Vega6, Eva Martínez7, Jaume Giménez8, Daniel Castrillejo9, Amparo Larrauri10. 1. National Centre of Epidemiology, Institute of Health Carlos III, Spain. Electronic address: amgherasim@externos.isciii.es. 2. National Centre for Microbiology, National Influenza Reference Laboratory, WHO-National Influenza Centre, Institute of Health Carlos III, Spain. Electronic address: pacopozo@isciii.es. 3. National Centre of Epidemiology, Institute of Health Carlos III, Spain; CIBER Epidemiología y Salud Pública (CIBERESP), Institute of Health Carlos III, Spain. Electronic address: smateo@isciii.es. 4. Subdirección de Salud Pública y Adicciones de Bizkaia, Pais Vasco, Spain. Electronic address: enfer4bi-san@euskadi.eus. 5. CIBER Epidemiología y Salud Pública (CIBERESP), Institute of Health Carlos III, Spain; Instituto de Salud Pública, Navarra Institute for Health Research (IdiSNA), Pamplona, Spain. Electronic address: mgcenoz@cfnavarra.es. 6. Dirección General de Salud Pública, Consejería de Sanidad de Castilla y León, Valladolid, Spain. Electronic address: VegAloTo@jcyl.es. 7. Servicio de Epidemiología y Prevención Sanitaria, Dirección General de Salud Pública y Consumo de La Rioja, La Rioja, Spain. Electronic address: emochoa@larioja.org. 8. Servicio de Epidemiología, Dirección General de Salut Pública, Mallorca, Baleares, Spain. Electronic address: jgimenez@dgsanita.caib.es. 9. Servicio de Epidemiología. DGSC, Consejería de Bienestar Social y Sanidad, Ciudad Autónoma de Melilla, Spain. Electronic address: dcastr01@melilla.es. 10. National Centre of Epidemiology, Institute of Health Carlos III, Spain; CIBER Epidemiología y Salud Pública (CIBERESP), Institute of Health Carlos III, Spain. Electronic address: alarrauri@isciii.es.
Abstract
INTRODUCTION: The 2014/15 influenza season in Spain was dominated by the circulation of drifted A(H3N2) and co-circulation of B viruses. We present the final estimates of influenza vaccine effectiveness (IVE) against confirmed influenza A(H3N2) and B its evolution along the season and with time since vaccination. METHODS: We used data collected on influenza like illness patients (ILI), systematically swabbed for the presence of influenza viruses within the Spanish Influenza Sentinel Surveillance System (SISS) and a restricted observational study (cycEVA). We used a test negative case-control design to compare influenza confirmed cases with negative controls. We estimated the IVE through a logistic regression model adjusting for potential confounders. The evolution of IVE was studied in early and late stages of the epidemic, and in different time intervals between receiving influenza vaccination and the onset of symptoms. RESULTS: At the end of the season we have found low and moderate IVE point estimates against influenza A(H3N2) and B, respectively, in all ages and target groups for vaccination. An IVE decreased from an early value of 37% to a late of -76% against influenza A(H3N2), and similarly, 84% vs -4% against Influenza B. When the onset of symptoms occurred more than three months after vaccination, the decrease of IVE was slower and milder against influenza B than against influenza A(H3N2). No significant change in the percentage of circulating drifted influenza A(H3N2) strains belonging to the 3c.2a and 3c.3a clades could be identified through the season. CONCLUSIONS: In a season dominated by drifted A(H3N2) circulating virus, the vaccine offered little or no protection against A(H3N2) infection but had a moderate protective effect against influenza B. Efforts should be put in developing influenza vaccines that maintain their protective capabilities throughout the season and could stimulate a potentially broad immune response against diverse influenza strains.
INTRODUCTION: The 2014/15 influenza season in Spain was dominated by the circulation of drifted A(H3N2) and co-circulation of B viruses. We present the final estimates of influenza vaccine effectiveness (IVE) against confirmed influenza A(H3N2) and B its evolution along the season and with time since vaccination. METHODS: We used data collected on influenza like illnesspatients (ILI), systematically swabbed for the presence of influenza viruses within the Spanish Influenza Sentinel Surveillance System (SISS) and a restricted observational study (cycEVA). We used a test negative case-control design to compare influenza confirmed cases with negative controls. We estimated the IVE through a logistic regression model adjusting for potential confounders. The evolution of IVE was studied in early and late stages of the epidemic, and in different time intervals between receiving influenza vaccination and the onset of symptoms. RESULTS: At the end of the season we have found low and moderate IVE point estimates against influenza A(H3N2) and B, respectively, in all ages and target groups for vaccination. An IVE decreased from an early value of 37% to a late of -76% against influenza A(H3N2), and similarly, 84% vs -4% against Influenza B. When the onset of symptoms occurred more than three months after vaccination, the decrease of IVE was slower and milder against influenza B than against influenza A(H3N2). No significant change in the percentage of circulating drifted influenza A(H3N2) strains belonging to the 3c.2a and 3c.3a clades could be identified through the season. CONCLUSIONS: In a season dominated by drifted A(H3N2) circulating virus, the vaccine offered little or no protection against A(H3N2) infection but had a moderate protective effect against influenza B. Efforts should be put in developing influenza vaccines that maintain their protective capabilities throughout the season and could stimulate a potentially broad immune response against diverse influenza strains.
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