title: Prevention of antigenically drifted influenza by inactivated and live attenuated vaccines.
abstract: BACKGROUND
  The efficacy of influenza vaccines may decline during years when the circulating viruses have antigenically drifted from those included in the vaccine.
  
  
  METHODS
  We carried out a randomized, double-blind, placebo-controlled trial of inactivated and live attenuated influenza vaccines in healthy adults during the 2004-2005 influenza season and estimated both absolute and relative efficacies.
  
  
  RESULTS
  A total of 1247 persons were vaccinated between October and December 2004. Influenza activity in Michigan began in January 2005 with the circulation of an antigenically drifted type A (H3N2) virus, the A/California/07/2004-like strain, and of type B viruses from two lineages. The absolute efficacy of the inactivated vaccine against both types of virus was 77% (95% confidence interval [CI], 37 to 92) as measured by isolating the virus in cell culture, 75% (95% CI, 42 to 90) as measured by either isolating the virus in cell culture or identifying it through real-time polymerase chain reaction, and 67% (95% CI, 16 to 87) as measured by either isolating the virus or observing a rise in the serum antibody titer. The absolute efficacies of the live attenuated vaccine were 57% (95% CI, -3 to 82), 48% (95% CI, -7 to 74), and 30% (95% CI, -57 to 67), respectively. The difference in efficacy between the two vaccines appeared to be related mainly to reduced protection of the live attenuated vaccine against type B viruses.
  
  
  CONCLUSIONS
  In the 2004-2005 season, in which most circulating viruses were dissimilar to those included in the vaccine, the inactivated vaccine was efficacious in preventing laboratory-confirmed symptomatic illnesses from influenza in healthy adults. The live attenuated vaccine also prevented influenza illnesses but was less efficacious. (ClinicalTrials.gov number, NCT00133523.)
authors.affiliation: Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor 48109, USA. sohmit@umich.edu
authors.forename: Suzanne E
authors.initials: SE
authors.lastname: Ohmit
authors.forename: John C
authors.initials: JC
authors.lastname: Victor
authors.forename: Judy R
authors.initials: JR
authors.lastname: Rotthoff
authors.forename: Esther R
authors.initials: ER
authors.lastname: Teich
authors.forename: Rachel K
authors.initials: RK
authors.lastname: Truscon
authors.forename: Laura L
authors.initials: LL
authors.lastname: Baum
authors.forename: Bhavya
authors.initials: B
authors.lastname: Rangarajan
authors.forename: Duane W
authors.initials: DW
authors.lastname: Newton
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Boulton
authors.forename: Arnold S
authors.initials: AS
authors.lastname: Monto
mesh_terms: D000293:Adolescent; D000328:Adult; D000956:Antigens, Viral / Q000235:genetics; D004311:Double-Blind Method; D005260:Female; D040961:Genetic Drift; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics / Q000276:immunology; D009981:Influenza B virus / Q000235:genetics / Q000276:immunology; D007252:Influenza Vaccines / Q000009:adverse effects; D007251:Influenza, Human / Q000517:prevention & control* / Q000821:virology; D008297:Male; D008875:Middle Aged; D016896:Treatment Outcome; D014613:Vaccines, Attenuated / Q000009:adverse effects; D015164:Vaccines, Inactivated / Q000009:adverse effects
chemical_list: D000956:Antigens, Viral; D007252:Influenza Vaccines; D014613:Vaccines, Attenuated; D015164:Vaccines, Inactivated