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.)
Monto
Arnold S
AS
Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI 48109, USA. asmonto@umich.edu
Ohmit
Suzanne E
SE
Petrie
Joshua G
JG
Johnson
Emileigh
E
Truscon
Rachel
R
Teich
Esther
E
Rotthoff
Judy
J
Boulton
Matthew
M
Victor
John C
JC
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