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Previous Volume 361:1260-1267 September 24, 2009 Number 13 Next

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ABSTRACT

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 [ClinicalTrials.gov] .)

Source Information

From the Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor (A.S.M., S.E.O., J.G.P., E.J., R.T., E.T., J.R., M.B.); and the Program for Appropriate Technology in Health (PATH), Seattle (J.C.V.).

Address reprint requests to Dr. Monto at the Department of Epidemiology, University of Michigan School of Public Health, 109 South Observatory St., M5156 SPH II, Ann Arbor, MI 48109, or at asmonto{at}umich.edu.

Full Text of this Article

Related Letters:

Comparative Efficacy of Influenza Vaccines
Narayan K.M. V., del Rio C., Linder J., Monto A., Ohmit S. E.
Extract | Full Text | PDF  
N Engl J Med 2010; 362:179-181, Jan 14, 2010. Correspondence

This article has been cited by other articles:

• Narayan, K.M. V., del Rio, C., Linder, J., Monto, A., Ohmit, S. E. (2010). Comparative Efficacy of Influenza Vaccines. NEJM 362: 179-181 [Full Text]  
• (2009). All you need to read in the other general journals. BMJ 339: b3945-b3945 [Full Text]  
• (2009). Comparative Efficacy of Seasonal Influenza Vaccines. JWatch Infect. Diseases 2009: 1-1 [Full Text]