I have been using Ace’s Tiger Repellant since 2009. I have NEVER been attacked by a tiger. Not even in a zoo or circus, and I have been to a circus and to several zoos since then.
My previous comment was NOT meant to dissuade anybody from getting a flu shot. In addition to it sometimes actually working, there is a lot of evidence that it will actually increase your immunity to a LOT of viruses for several months, whether or not it works 100% against the flu.