Why You Need an Annual Flu Shot
Childhood immunizations are common. A few shots before school, some boosters later. Mostly, you're done before you enter your teen years. You're completely protected for the rest of your life. So why do you need to get a flu shot every year?
It's a bit inaccurate to talk about the flu. In fact, it changes from season to season just as a child is slightly different from his or her parents. Each version protects itself from vaccines that were effective against previous versions.
Influenza actually changes in two ways from season to season. One way is simple mutation. As the virus copies its genetic information from one cell to another, small changes creep in, and eventually it becomes something that, while still flu, is otherwise unrecognizable. The other is by exchanging bits of genetic code with other, different viruses. This creates a completely different virus, one which is completely untouched by last year's vaccine.
If someone you spend time with has a weak immune system, such as because they're old, young, or taking medications that suppress immunity, you should get the shot. It won't just protect you, it will protect them.