The MS medication I've been shooting up with since August of 1998 is an interferon. The primary side effects of interferons are "flu-like" things such as fever, muscle aches, chills, blah, blah, blah. I learned tricks to minimize the effects, like popping Tylenol or Motrin prior to the injection, or doing the shot at night in an attempt to sleep through the worst of it. I've even gone so far as to get shitfaced drunk so I could pass out! Well, okay, I only did that once and the hangover was NOT worth it.
My point here is, I've been experiencing - or skating around - a remarkable facsimile of the flu, for approximately the last 540 weeks. The vaccine ought to be a cakewalk.