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Previous Volume 355:2513-2522 December 14, 2006 Number 24 Next

	Full Text PDF PDA Full Text PowerPoint Slide Set Editorial by Fukuda, K. Add to Personal Archive Add to Citation Manager Notify a Friend E-mail When Cited E-mail When Letters Appear

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 [ClinicalTrials.gov] .)

Source Information

From the Department of Epidemiology, University of Michigan School of Public Health (S.E.O., J.C.V., J.R.R., E.R.T., R.K.T., L.L.B., B.R., D.W.N., M.L.B., A.S.M.); and the Department of Pathology–Virology, University of Michigan Hospitals (D.W.N.) — both in Ann Arbor.

Address reprint requests to Dr. Ohmit at the University of Michigan School of Public Health, 109 Observatory St., Ann Arbor, MI 48109, or at sohmit{at}umich.edu.

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