Flu shots are quite controversial. Of all the vaccines we are asked to get, influenza is the only one that has to be given every year and has a much lower efficacy rate than most others. It's understandable that people are wary or confused about whether or not it is even worth getting. The truth is, flu vaccines don't always work. It would be great if they did, but they don't. Here are a few reasons why they might not work every single time.