Comparative efficacy of inactivated and live attenuated influenza vaccines.
BACKGROUND
The efficacy of influenza vaccines may vary from year to year, depending on a variety of factors, and may differ for inactivated and live attenuated vaccines.


METHODS
We carried out a randomized, double-blind, placebo-controlled trial of licensed inactivated and live attenuated influenza vaccines in healthy adults during the 2007-2008 influenza season and estimated the absolute and relative efficacies of the two vaccines.


RESULTS
A total of 1952 subjects were enrolled and received study vaccines in the fall of 2007. Influenza activity occurred from January through April 2008, with the circulation of influenza types A (H3N2) (about 90%) and B (about 9%). Absolute efficacy against both types of influenza, as measured by isolating the virus in culture, identifying it on real-time polymerase-chain-reaction assay, or both, was 68% (95% confidence interval [CI], 46 to 81) for the inactivated vaccine and 36% (95% CI, 0 to 59) for the live attenuated vaccine. In terms of relative efficacy, there was a 50% (95% CI, 20 to 69) reduction in laboratory-confirmed influenza among subjects who received inactivated vaccine as compared with those given live attenuated vaccine. The absolute efficacy against the influenza A virus was 72% (95% CI, 49 to 84) for the inactivated vaccine and 29% (95% CI, -14 to 55) for the live attenuated vaccine, with a relative efficacy of 60% (95% CI, 33 to 77) for the inactivated vaccine.


CONCLUSIONS
In the 2007-2008 season, the inactivated vaccine was efficacious in preventing laboratory-confirmed symptomatic influenza A (predominately H3N2) in healthy adults. The live attenuated vaccine also prevented influenza illnesses but was less efficacious. (ClinicalTrials.gov number, NCT00538512.)
Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI 48109, USA. asmonto@umich.edu
Arnold S
AS
Monto
Suzanne E
SE
Ohmit
Joshua G
JG
Petrie
Emileigh
E
Johnson
Rachel
R
Truscon
Esther
E
Teich
Judy
J
Rotthoff
Matthew
M
Boulton
John C
JC
Victor
D000293:Adolescent; D000328:Adult; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D015994:Incidence; D053122:Influenza A Virus, H3N2 Subtype / Q000302:isolation & purification; D009981:Influenza B virus / Q000302:isolation & purification; D007252:Influenza Vaccines / Q000009:adverse effects / Q000276:immunology*; D007251:Influenza, Human / Q000276:immunology / Q000517:prevention & control* / Q000821:virology; D008297:Male; D012306:Risk; D016896:Treatment Outcome; D014613:Vaccines, Attenuated / Q000009:adverse effects / Q000276:immunology; D015164:Vaccines, Inactivated / Q000009:adverse effects / Q000276:immunology; D055815:Young Adult
D007252:Influenza Vaccines; D014613:Vaccines, Attenuated; D015164:Vaccines, Inactivated