Answer: Our bodies, when they encounter a foreign invader, will generate VERY specific antibodies that are made to disable ONLY that foreign invader. It's like this flu virus has a disguise, and our bodies don't recognize the virus (even though it fights it off almost every year), so we get sick again. Getting immunized for the flu virus is vital because they can form temporary antibodies and resist the virus. But of course, there's always the chance that the vaccine will be very off and you can get sick again.
Explanation: i hope this helps