Background. Influenza is a significant cause of morbidity, and vaccination is the preferred preventive strategy. Data regarding the preferred influenza vaccine type among adults are limited.
Methods. The effectiveness of 2 currently available influenza vaccines LAIV and TIV in preventing influenza-like illness (ILI) was compared among US military members (aged 18–49 years) during 3 consecutive influenza seasons (2006–2009). ILI, influenza, and pneumonia events post-vaccination were compared between vaccine types using Cox proportional hazard models adjusted for sociodemographic factors, occupation, and geographic area.
Results. A total of 41 670 vaccination events were evaluated, including 28 929 during 2 “well-matched” seasons (2006–2007 and 2008–2009: LAIV n = 22 734, TIV n = 6195) and 12 741 during a suboptimally matched season due to mild antigenic drift (2007–2008: LAIV n = 9447, TIV n = 3294). ILI crude incidence rates for LAIV and TIV were 139 and 127 cases per 1000 person-seasons for the well-matched seasons, respectively, and 150 and 165 cases per 1000 person-seasons for the suboptimally matched season, respectively. In the multivariable models, there were no differences in ILI events by vaccine type (well-matched seasons: hazard ratio [HR], 0.97; 95% confidence interval [CI], .90–1.06; suboptimally matched season: HR, 1.00; 95% CI, .90–1.11). There were also no differences in influenza and/or pneumonia events by vaccine group.
Conclusions. Between 2006 and 2009, TIV and LAIV had similar effectiveness in preventing ILI and influenza/pneumonia events among healthy adults.