"There are risks versus benefits considerations and decisions all the time in our lives every day. Do you drive a car? There's approximately one traffic death for every million miles driven in the USA, similar to the risk to GBS occurring post vaccination. Admittedly, the benefit of the flu vaccine is variable from year to year as the flu type(s) selected for the vaccine each year has always been predictive. It's an educated guess that involves complex historical epidemiological statistical analysis of flu type trends throughout the world."