Learning Objectives for this Presentation:
By the end of the presentation participant will be able to: a. better understand the safety profile of influenza vaccine.
b. learn about most frequently reported adverse events following influenza vaccination.


Background:
Annual influenza vaccination in adults is the most widely used vaccine in the US. Assuring the safety of influenza vaccine is a critical public health function. The Vaccine Adverse Events Reporting System (VAERS) is a spontaneous reporting system for adverse events (AEs) of US licensed vaccines and the only national system for the timely detection of possible rare or unusual vaccine AEs.

Objectives:
Evaluate reporting trends of serious and non-serious reports and most frequently reported AEs following influenza vaccination in adults.

Methods:
We selected all influenza reports to VAERS from July 1, 1990 to June 30, 2004 in adults (>18 years). Influenza season was defined as the period from July 1-June 30. To calculate AE reporting rates, we used denominator data estimated from the National Health Interview Survey and the US population census. Reports were grouped into three age-group categories (18-49, 50-64 and >65 years) and according to serious and non-serious reports. We used Poisson regression for linear trend to evaluate age-adjusted trends over time.

Results:
From July 1, 1990 through June 30, 2004 VAERS received 16,649 reports following influenza vaccine, including 2,276 serious reports and over 630 million persons received influenza vaccine. The most frequently reported serious AE in all age-groups was Guilain-Barre Syndrome (21%) and for non-serious AEs it was injection site reactions (22%). Overall, and in the age-groups 50-64 and >65 years, we observed a significant decline in all serious AEs reporting rate (p <.001) including Guilain-Barre Syndrome. In contrast, we observed a significant increase in reporting rate of non-serious AEs overall (p<. 001) and in age-groups 18-49 and >65 years.

Conclusions:
The decrease in reporting rates for serious AEs provide reassurance on the safety of influenza vaccine. Many factors may contribute to the increases in non-serious reports which may require further analysis.