title: Clinical effectiveness of split-virion versus subunit trivalent influenza vaccines in older adults.
abstract: BACKGROUND
  Inactivated influenza vaccines are manufactured using either split-virion or subunit methods. These 2 methods produce similar hemagglutinin antibody responses, but different cellular immune responses.
  
  
  METHODS
  We compared the effectiveness of split-virion influenza vaccines to that of subunit influenza vaccines using prospectively collected data from adults aged ≥50 years who sought care for acute respiratory illness during 3 influenza seasons: 2008-2009, 2010-2011, and 2011-2012 using a case-positive, control test-negative study design.
  
  
  RESULTS
  Complete data were available for 539 participants, of whom 68 (12.6%) had influenza detected. Influenza-infected patients were younger (P<.001), were more likely to have received no vaccine or the subunit influenza vaccine than the split-virion vaccine (P<.001), and more likely to have sought care in either the emergency department or the acute care clinic than the hospital (P=.001). Split-virion vaccine effectiveness was 77.8% (95% confidence interval [CI], 58.5%-90.3%) compared with subunit vaccine effectiveness of 44.2% (95% CI, -11.8% to 70.9%), giving a difference in vaccine effectiveness of 33.5% (95% CI, 6.9%-86.7%).
  
  
  CONCLUSIONS
  Studies need to be done to further explore if there are differences in clinical effectiveness in older adults for the 2 vaccine manufacturing methods.
authors.affiliation: Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: H Keipp
authors.initials: HK
authors.lastname: Talbot
authors.affiliation: Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Hui
authors.initials: H
authors.lastname: Nian
authors.affiliation: Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Yuwei
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Qingxia
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: John V
authors.initials: JV
authors.lastname: Williams
authors.affiliation: Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Marie R
authors.initials: MR
authors.lastname: Griffin
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D007251:Influenza, Human / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D016896:Treatment Outcome; D015164:Vaccines, Inactivated / Q000008:administration & dosage / Q000276:immunology; D022223:Vaccines, Subunit / Q000008:administration & dosage / Q000276:immunology
chemical_list: D007252:Influenza Vaccines; D015164:Vaccines, Inactivated; D022223:Vaccines, Subunit
keywords: clinical effectiveness; influenza; older adults; split-virion vaccine; subunit vaccine