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Randomized Controlled Trial
. 2008 Aug 1;198(3):312-7.
doi: 10.1086/589885.

Prevention of symptomatic seasonal influenza in 2005-2006 by inactivated and live attenuated vaccines

Suzanne E Ohmit  1 , John C Victor, Esther R Teich, Rachel K Truscon, Judy R Rotthoff, Duane W Newton, Sarah A Campbell, Matthew L Boulton, Arnold S Monto
Affiliations
Randomized Controlled Trial

Prevention of symptomatic seasonal influenza in 2005-2006 by inactivated and live attenuated vaccines

Suzanne E Ohmit et al. J Infect Dis. .

Abstract

Background: The efficacy of influenza vaccines may vary annually. In 2004-2005, when antigenically drifted viruses were circulating, a randomized, placebo-controlled trial involving healthy adults showed that inactivated vaccine appeared to be efficacious, whereas live attenuated vaccine appeared to be less so.

Methods: In 2005-2006, we continued our trial, examining the absolute and relative efficacies of the live attenuated and inactivated vaccines in preventing laboratory-confirmed symptomatic influenza.

Results: A total of 2058 persons were vaccinated in October and November 2005. Studywide influenza activity was prolonged but of low intensity; type A (H3N2) virus was circulating, which was antigenically similar to the vaccine strain. The absolute efficacy of the inactivated vaccine was 16% (95% confidence interval [CI], -171% to 70%) for the virus identification end point (virus isolation in cell culture or identification through polymerase chain reaction) and 54% (95% CI, 4%-77%) for the primary end point (virus isolation or increase in serum antibody titer). The absolute efficacies of the live attenuated vaccine for these end points were 8% (95% CI, -194% to 67%) and 43% (95% CI, -15% to 71%), respectively.

Conclusions: With serologic end points included, efficacy was demonstrated for the inactivated vaccine in a year with low influenza attack rates. The efficacy of the live attenuated vaccine was slightly less than that of the inactivated vaccine, but not statistically greater than that of the placebo.

Trial registration: ClinicalTrials.gov NCT00133523.

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Conflict of interest statement

Potential conflicts of interest: J.C.V. reports receiving consulting fees from Wyeth. A.S.M. reports receiving consulting fees from GlaxoSmithKline, MedIm-mune, Solvay, and Novartis, and an unrestricted research grant from Sanofi-Pasteur. No other authors report any potential conflicts of interest relevant to this article.

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