Effectiveness of Live Attenuated Influenza Vaccine and Inactivated Influenza Vaccines in Active Duty Members of the US Military
Background: Most studies assessing the relative effectiveness of live attenuated influenza vaccine (LAIV) and inactivated influenza vaccine (IIV) in adults have demonstrated that vaccines were similarly effective or IIV was more effective. Studies have suggested that relative effectiveness may vary by season and population characteristics. This study evaluated effect modifiers of the relative effectiveness of LAIV vs IIV against influenza-like illness (ILI) in adults vaccinated in the US military during 2010–2011.
Methods: Active duty members of the US military aged 18–49 years, stationed in the contiguous United States were followed from November 21, 2010 (start of the influenza season) until occurrence of ILI, season end (April 16, 2011), or censoring event, whichever came first. To help ensure comparability of LAIV and IIV recipients, individuals with asthma, chronic bronchitis, emphysema, shortness of breath, diabetes mellitus, HIV infection, or pregnancy were excluded. Data were obtained from the Department of Defense Military Health System database, a relational database containing longitudinal data on demographic characteristics and medical encounters of service members.
Results: A total of 90,084 LAIV recipients and 50,098 IIV recipients were identified. Cumulative incidence rates of ILI are presented in the Figure. The risk of ILI during the influenza season was higher among IIV recipients (14.0%) than among LAIV recipients (12.6%), yielding a hazard ratio (HR) of 1.12 (95% CI: 1.09, 1.16). LAIV relative effectiveness versus IIV was greater among those vaccinated with IIV in the prior season (HR: 1.29 [95% CI: 1.19, 1.39]) than among those vaccinated with LAIV in the prior season (HR: 1.05 [95% CI: 0.99, 1.11]. No other significant effect modification was observed as a function of gender, class of age, exposure to tobacco, or other baseline characteristics.
Conclusion: The type of influenza vaccine received in the prior year was a significant effect modifier of the LAIV relative effectiveness versus IIV in adults, with LAIV relative effectiveness higher among IIV recipients in the prior season. The validity and generalizibility of this finding will be examined in data from additional seasons.
This study was sponsored by MedImmune.
MedImmune: Employee, I am a full time employee of MedImmune and Salary
N. M. Sicignano, MedImmune, LLC: Collaborator, Research support
C. S. Ambrose, Astrazeneca: Employee, Salary