Background: Trivalent live attenuated influenza vaccine (LAIV3) was licensed and recommended for use in 2003 in children and adults 2-49 years of age. Post-licensure safety data have been limited, particularly in adults.

Methods: We searched Vaccine Adverse Event Reporting System (VAERS) for US reports after LAIV3 from July 1, 2005-June 30, 2013 (eight influenza seasons) in adults aged ≥ 18 years old. We conducted descriptive analyses and clinically reviewed serious reports (i.e., death, life-threatening illness, hospitalization, prolonged hospitalization, or permanent disability) and reports of selected conditions of interest. We used empirical Bayesian data mining to identify adverse events (AEs) that were reported more frequently than expected. We calculated crude AE reporting rates to VAERS by influenza season.

Results: During the study period, VAERS received 1207 LAIV3 reports in adults aged 18-49 years old; 107 (8.9%) were serious, including four death reports. The most commonly reported events were expired drug administered (n=207, 17%), headache (n=192, 16%), and fever (n=133, 11%). The most common diagnostic categories for non-fatal serious reports were neurological (n=40, 39%), cardiovascular (n=14, 14%), and other non-infectious conditions (n=20, 19%). We noted a higher proportion of Guillain-Barré syndrome (GBS) and cardiovascular reports in the Department of Defense (DoD) population compared to the civilian population. Data mining detected disproportional reporting of ataxia (n=15); clinical review revealed that ataxia was a component of diverse clinical entities including GBS.

Conclusions: Review of VAERS reports are reassuring, the only unexpected safety concern for LAIV3 identified was a higher than expected number of GBS reports in the DoD population, which is being investigated. Reports of administration of expired LAIV3 represent administration errors and indicate the need for education, training and screening regarding the approved indications.