Effectiveness of Influenza Vaccine for Preventing Laboratory-Confirmed Influenza Hospitalizations in Adults, 2011-2012 Influenza Season

During the 2011-2012 influenza season, we enrolled hospitalized adults with acute respiratory illness and tested each for influenza using reverse transcription polymerase chain reaction. Influenza vaccination was verified in 35% (6/17) of adults with influenza-associated hospitalizations compared to 64% (97/152) of test-negative controls; adjusted vaccine effectiveness was 71.4% (95% confidence interval, 17.1%-94.9%).