title: Waning protection of influenza vaccine against mild laboratory confirmed influenza A(H3N2) and B in Spain, season 2014-15.
abstract: BACKGROUND
  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.
authors.affiliation: National Centre of Epidemiology, Institute of Health Carlos III, Spain. Electronic address: amgherasim@externos.isciii.es.
authors.forename: Alin
authors.initials: A
authors.lastname: Gherasim
authors.affiliation: National Centre for Microbiology, National Influenza Reference Laboratory, WHO-National Influenza Centre, Institute of Health Carlos III, Spain. Electronic address: pacopozo@isciii.es.
authors.forename: Francisco
authors.initials: F
authors.lastname: Pozo
authors.affiliation: 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.
authors.forename: Salvador
authors.initials: S
authors.lastname: de Mateo
authors.affiliation: Subdirección de Salud Pública y Adicciones de Bizkaia, Pais Vasco, Spain. Electronic address: enfer4bi-san@euskadi.eus.
authors.forename: Inma Aspiritxaga
authors.initials: IA
authors.lastname: Gamarra
authors.affiliation: 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.
authors.forename: Manuel
authors.initials: M
authors.lastname: García-Cenoz
authors.affiliation: Dirección General de Salud Pública, Consejería de Sanidad de Castilla y León, Valladolid, Spain. Electronic address: VegAloTo@jcyl.es.
authors.forename: Tomas
authors.initials: T
authors.lastname: Vega
authors.affiliation: Servicio de Epidemiología y Prevención Sanitaria, Dirección General de Salud Pública y Consumo de La Rioja, La Rioja, Spain. Electronic address: emochoa@larioja.org.
authors.forename: Eva
authors.initials: E
authors.lastname: Martínez
authors.affiliation: Servicio de Epidemiología, Dirección General de Salut Pública, Mallorca, Baleares, Spain. Electronic address: jgimenez@dgsanita.caib.es.
authors.forename: Jaume
authors.initials: J
authors.lastname: Giménez
authors.affiliation: Servicio de Epidemiología. DGSC, Consejería de Bienestar Social y Sanidad, Ciudad Autónoma de Melilla, Spain. Electronic address: dcastr01@melilla.es.
authors.forename: Daniel
authors.initials: D
authors.lastname: Castrillejo
authors.affiliation: 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.
authors.forename: Amparo
authors.initials: A
authors.lastname: Larrauri
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000940:Antigenic Variation; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053122:Influenza A Virus, H3N2 Subtype; D009981:Influenza B virus; D007252:Influenza Vaccines / Q000627:therapeutic use*; D007251:Influenza, Human / Q000517:prevention & control*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D018571:Sentinel Surveillance; D013030:Spain / Q000453:epidemiology; D014611:Vaccination / Q000706:statistics & numerical data*; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: Influenza; Influenza vaccine; Influenza-like illness; Test negative case–control design; Vaccine effectiveness; Waning protection