FluMist is a live, intranasal influenza vaccine produced by MedImmune. You may have seen this season's commercials with the tagline "Pick your nose".
People always worry about getting the flu from flu shots. Now, there is no way you can get the flu from a flu shot because it's a dead virus. You can FEEL like you have the flu for a day or so because most of what makes having the flu so miserable is your immune system taking no prisoners trying to kill the flu virus. If you have a good, healthy immune system (which we all hope we do) it will jump on those bits of dead flu virus just as if it was a real invader. By doing that, it is put on high alert and will stop and kill any real flu viruses you may be exposed to before they do any harm. So really, it's a good thing if you feel like crap after your flu shot.
FluMist, now, IS a live virus. Its makers HOPE that it will replicate in you. Why is this ok? Well, FluMist is live, but it is attenuated (or weakened), so that it cannot cause illness. It is also cold-adapted; that means it has been altered so that it replicates best in the colder temperatures of your nasopharynx (the hollow between your nose and your throat). The tissues of the nasopharynx are the body's first line of defense against the flu or any other respiratory infection. Also, FluMist is temperature-sensitive; this means it cannot grow at normal body temperature and will die if it tries to invade the lungs. There are 5 different mutations that have been engineered to ensure these characteristics (attenuation, cold adaptation, temperature sensitivity). Each of these mutations has a 1 in a million chance of spontaneously reversing, and all 5 would have to spontaneously reverse to change this back into a disease-causing organism. I'll leave it to our resident math or statistics majors to figure out what the chances of that happening is; my mind really can't deal with that large of a number, so I'll just say it's one in a bajillion.
Common adverse reactions (logically, if you have this replicating in your nose) are runny nose and congestion, low-grade fever, and sore throat.
FluMist has been out for 7 years now, and I'm quite impressed by its efficacy. As a matter of fact, that's what my kids have gotten the last 3 flu seasons. It protects against influenza approximately twice as well as the regular flu shot, and it actually gives some increased protection against non-matched (i.e. the experts didn't guess right) strains of flu. It's easy to do, completely painless and nontraumatic for the kids, and works better. No-brainer in my book...
FluMist is grown in chicken eggs, so if you're allergic to eggs (or Gentamicin and gelatin, because they use that too) you should talk to your allergist before getting the shot. Also, if you're under 18 and take aspirin or salicylate-containing products you should talk to your doctor as well before taking any live-virus vaccines, since there is a tiny risk of Reye's Syndrome. However, you should definitely get SOME kind of flu shot because there is a much bigger risk of getting Reye's Syndrome if you CATCH the flu. If you've ever had an allergic reaction to a flu shot, you shouldn't be getting this one either.
The studies of FluMist found that there was a higher incidence of wheezing in kids under 2, so it's a risk-benefit analysis whether you want to get your 6 month to 2 year old child stuck or get them FluMist - once again, talk to your doctor, but get them protected. It's also not (technically) recommended for people over 50, because they weren't included in the studies they did, so the FDA makes them say that.
FluMist seminar at the Indiana School Nurse Association annual conference
personal communications with Dr. Belcher, Infectious Disease Specialist