title: Influenza Vaccine Effectiveness Against Antigenically Drifted Influenza Higher Than Expected in Hospitalized Adults: 2014-2015.
abstract: The 2014-2015 influenza season was severe, with circulating influenza A (H3N2) viruses that were antigenically drifted from the vaccine virus. Reported vaccine effectiveness (VE) estimates from ambulatory care settings were markedly decreased.
  
  
  
  Adults, hospitalized at 2 hospitals in southeast Michigan for acute respiratory illnesses, defined by admission diagnoses, of ≤10 days duration were prospectively enrolled. Throat and nasal swab specimens were collected, combined, and tested for influenza by real-time reverse transcription polymerase chain reaction. VE was estimated by comparing the vaccination status of those testing positive for influenza with those testing negative in logistic regression models adjusted for age, sex, hospital, calendar time, time from illness onset to specimen collection, frailty score, and Charlson comorbidity index (CCI).
  
  
  
  Among 624 patients included in the analysis, 421 (68%) were vaccinated, 337 (54%) were female, 220 (35%) were age ≥65 years, and 92% had CCI > 0, indicating ≥1 comorbid conditions. Ninety-eight (16%) patients tested positive for influenza A (H3N2); among 60 (61%) A (H3N2) viruses tested by pyrosequencing, 53 (88%) belonged to the drifted 3C.2a genetic group. Adjusted VE was 43% (95% confidence interval [CI], 4-67) against influenza A (H3N2); 40% (95% CI, -13 to 68) for those <65 years, and 48% (95% CI, -33 to 80) for those ≥65 years. Sensitivity analyses largely supported these estimates.
  
  
  
  VE estimates appeared higher than reports from similar studies in ambulatory care settings, suggesting that the 2014-2015 vaccine may have been more effective in preventing severe illness requiring hospitalization.
authors.affiliation: Department of Epidemiology, University of Michigan, School of Public Health.
authors.forename: Joshua G
authors.initials: JG
authors.lastname: Petrie
authors.affiliation: Department of Epidemiology, University of Michigan, School of Public Health.
authors.forename: Suzanne E
authors.initials: SE
authors.lastname: Ohmit
authors.affiliation: Department of Epidemiology, University of Michigan, School of Public Health.
authors.forename: Caroline K
authors.initials: CK
authors.lastname: Cheng
authors.affiliation: Department of Epidemiology, University of Michigan, School of Public Health.
authors.forename: Emily T
authors.initials: ET
authors.lastname: Martin
authors.affiliation: Department of Epidemiology, University of Michigan, School of Public Health.
authors.forename: Ryan E
authors.initials: RE
authors.lastname: Malosh
authors.affiliation: Department of Microbiology and Immunology Department of Internal Medicine, Division of Infectious Diseases, University of Michigan, Ann Arbor.
authors.forename: Adam S
authors.initials: AS
authors.lastname: Lauring
authors.affiliation: Department of Public Health Sciences.
authors.forename: Lois E
authors.initials: LE
authors.lastname: Lamerato
authors.affiliation: Department of Medicine, Division of Infectious Diseases, Henry Ford Health System, Detroit, Michigan.
authors.forename: Katherine C
authors.initials: KC
authors.lastname: Reyes
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Brendan
authors.initials: B
authors.lastname: Flannery
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Jill M
authors.initials: JM
authors.lastname: Ferdinands
authors.affiliation: Department of Epidemiology, University of Michigan, School of Public Health.
authors.forename: Arnold S
authors.initials: AS
authors.lastname: Monto
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000940:Antigenic Variation; D016022:Case-Control Studies; D015897:Comorbidity; D005260:Female; D049674:History, 21st Century; D006760:Hospitalization; D006801:Humans; D009980:Influenza A virus / Q000276:immunology*; D007252:Influenza Vaccines / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology* / Q000266:history / Q000517:prevention & control*; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: antigenic drift; case test-negative design; hospital; influenza A (H3N2); influenza vaccine effectiveness