title: Influenza vaccine effectiveness in preventing hospitalizations with laboratory-confirmed influenza in Greece during the 2014-2015 season: A test-negative study.
abstract: The 2014-2015 influenza season was marked by circulation of antigenically drifted A/H3N2 strains, raising the possibility of low seasonal influenza Vaccine Effectiveness (VE). We assessed VE against hospitalization with laboratory-confirmed influenza for the 2014-2015 season, using routine surveillance data. Non-sentinel swab samples from Greek hospital inpatients were tested for influenza by RT-PCR in three laboratories, covering the entire country. We estimated VE using a test-negative design. Out of 883 patients with known vaccination status, 161 (18.2%) were vaccinated, and 392/883 patients (44.4%) tested positive for influenza, of whom 162 (41.3%) had type B and 151 (38.5%) had A/H3N2. Adjusted VE was 31.6% (95%CI: 2.9-51.8%) against any influenza, 46.8%, 95%CI: 12.5-67.6%) against type B and -1.9%, 95%CI: -69.5 to 38.7%) against A/H3N2. VE against non-ICU hospitalization appeared to be higher, but the difference did not reach statistical significance. Circulating A/H3N2 viruses showed substantial antigenic drift, while about half of the type B strains were similar to the vaccine strain. Despite the antigenic drift of the A/H3N2 strains, the vaccine still offered substantial protection against hospitalization with laboratory-confirmed influenza, mostly due to a surge in type B influenza late in the season. Vaccine coverage was low, even among groups targeted for vaccination, and considerable effort should be made to improve it. J. Med. Virol. 88:1896-1904, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Epidemiological Surveillance and Intervention, Hellenic Centre for Disease Control and Prevention, Athens, Greece.|Centre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain.|Department of Experimental and Health Sciences, Universitat Pompeu Fabra (UPF), Barcelona, Spain.
authors.forename: Theodore
authors.initials: T
authors.lastname: Lytras
authors.affiliation: National Influenza Reference Laboratory for Southern Greece, Hellenic Pasteur Institute, Athens, Greece.
authors.forename: Athanasios
authors.initials: A
authors.lastname: Kossyvakis
authors.affiliation: National Influenza Reference Laboratory for Northern Greece, Medical School, Aristotle University of Thessaloniki, Thessaloniki, Greece.
authors.forename: Angeliki
authors.initials: A
authors.lastname: Melidou
authors.affiliation: Department of Epidemiological Surveillance and Intervention, Hellenic Centre for Disease Control and Prevention, Athens, Greece.
authors.forename: Anastasia
authors.initials: A
authors.lastname: Andreopoulou
authors.affiliation: National Influenza Reference Laboratory for Northern Greece, Medical School, Aristotle University of Thessaloniki, Thessaloniki, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Exindari
authors.affiliation: National Influenza Reference Laboratory for Northern Greece, Medical School, Aristotle University of Thessaloniki, Thessaloniki, Greece.
authors.forename: Georgia
authors.initials: G
authors.lastname: Gioula
authors.affiliation: National Influenza Reference Laboratory for Southern Greece, Hellenic Pasteur Institute, Athens, Greece.
authors.forename: Antonios
authors.initials: A
authors.lastname: Kalliaropoulos
authors.affiliation: Antimicrobial Resistance and Health Associated Infections Laboratory, Central Public Health Laboratory, Hellenic Centre for Disease Control and Prevention, Athens, Greece.|European Public Health Microbiology Training programme (EUPHEM), European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden.
authors.forename: Kyriaki
authors.initials: K
authors.lastname: Tryfinopoulou
authors.affiliation: National Influenza Reference Laboratory for Southern Greece, Hellenic Pasteur Institute, Athens, Greece.
authors.forename: Vasiliki
authors.initials: V
authors.lastname: Pogka
authors.affiliation: Department of Epidemiological Surveillance and Intervention, Hellenic Centre for Disease Control and Prevention, Athens, Greece.
authors.forename: Georgia
authors.initials: G
authors.lastname: Spala
authors.affiliation: National Influenza Reference Laboratory for Northern Greece, Medical School, Aristotle University of Thessaloniki, Thessaloniki, Greece.
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Malisiovas
authors.affiliation: National Influenza Reference Laboratory for Southern Greece, Hellenic Pasteur Institute, Athens, Greece.
authors.forename: Andreas
authors.initials: A
authors.lastname: Mentis
mesh_terms: D000293:Adolescent; D000328:Adult; D000956:Antigens, Viral / Q000235:genetics; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D019411:Clinical Laboratory Techniques; D062665:Epidemiological Monitoring; D005260:Female; D040961:Genetic Drift; D006115:Greece / Q000453:epidemiology; D006760:Hospitalization; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics / Q000276:immunology; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics / Q000276:immunology; D009981:Influenza B virus / Q000276:immunology; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D007251:Influenza, Human / Q000175:diagnosis* / Q000453:epidemiology / Q000517:prevention & control* / Q000821:virology; D008297:Male; D008875:Middle Aged; D012107:Research Design; D012621:Seasons; D014611:Vaccination; D064166:Vaccine Potency; D055815:Young Adult
chemical_list: D000956:Antigens, Viral; D007252:Influenza Vaccines
keywords: epidemiology; immunity/immunization; influenza virus; seasonal incidence; surveillance; vaccine effectiveness; vaccines/vaccine strains