The first time that I ever got a flu shot I felt like I immediately got sick. 4 hours after it, I had all the symptoms of the flu.
So I blamed it and hated flu shots for a while.
But then I realized: the flu shot could not have given me the flu, unless it was magic.
Think about it: There's at least 24 hours of incubation for the flu, usually 48 or more, for any kind of viral infection...*nothing* injected into you can cause symptoms that fast. It isn't possible.
(Even if someone injected you with smallpox, you wouldn't get the symptoms of smallpox for 2-4 days after.)
So I asked a friend of mine, who is an Infectious Diseases Specialist at OHSU..he said,
-It takes an entire week for the flu shot to really protect you.
-It does so by introducing your immune system to dead flu virus cells.
-Your immune system encounters them, identifies them, and then starts to produce antibodies. (It's fooled into thinking it's a real infection.)
-It takes days for those antibodies to protect you...enough of them have to accumulate in your bloodstream for defense to work. (Good guys have to outnumber bad guys.)
So, what is happening when you get sick *right after* a flu shot?
-You already had contact with the flu, days earlier, and it was in its incubation period already inside you.
-The introduced *dead* flu virus that came with your flu shot activated your immune system.
-Your immune system thought you were infected earlier than it normally would have realized it due to the dead cells sounding a sort of "alarm" in your body.
-You get the symptoms of your infection right away, rather than later, because your body has now raised the alarm and gone into full-fledged war with the infection.
-A certain percentage of the population always has these "reactions" to a flu shot every now and then, because a certain percentage of the population has always been exposed to the flu before they get it.
The doc told me to get another flu shot, this time *before* the flu season really began, and he assured me I wouldn't have the same reaction. The odds would be really small.
He was right. And now I get them every year. I see poor saps around me in college coming down with it, and my family members...and I stay upright and fine.
I personally like getting the flu shot now and I don't care about the "brain damage" fear-mongering. Most doctors get the flu shot and you don't see legions of docs running around like Mad Hatters.