Prevention of symptomatic seasonal influenza in 2005-2006 by inactivated and live attenuated vaccines.
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.
University of Michigan School of Public Health, Department of Epidemiology, Ann Arbor, Michigan 48109, USA. sohmit@umich.edu
Suzanne E
SE
Ohmit
John C
JC
Victor
Esther R
ER
Teich
Rachel K
RK
Truscon
Judy R
JR
Rotthoff
Duane W
DW
Newton
Sarah A
SA
Campbell
Matthew L
ML
Boulton
Arnold S
AS
Monto
D000293:Adolescent; D000328:Adult; D000914:Antibodies, Viral / Q000097:blood; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype / Q000302:isolation & purification; D007252:Influenza Vaccines / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control* / Q000821:virology; D008297:Male; D008875:Middle Aged; D010919:Placebos / Q000008:administration & dosage; D014613:Vaccines, Attenuated / Q000276:immunology; D015164:Vaccines, Inactivated / Q000276:immunology
D000914:Antibodies, Viral; D007252:Influenza Vaccines; D010919:Placebos; D014613:Vaccines, Attenuated; D015164:Vaccines, Inactivated