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Randomized Controlled Trial
. 2006 Dec 14;355(24):2513-22.
doi: 10.1056/NEJMoa061850.

Prevention of antigenically drifted influenza by inactivated and live attenuated vaccines

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

Prevention of antigenically drifted influenza by inactivated and live attenuated vaccines

Suzanne E Ohmit et al. N Engl J Med. .

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.)

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Figures

Figure 1
Figure 1
Enrollment and Follow-up of Study Participants during the 2004–2005 Influenza Season in Michigan.
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