Can You Get the Flu Shot from the Flu

The widespread belief that the flu shot can cause the flu reminds me of the old story among teenagers that Mountain Dew can prevent pregnancy. Because these myths are repeated so often, people start believing they are true.

The truth is the only way you can get the flu right after getting the flu shot is if you contract the virus at about the same time you get the flu shot. The coincidence in timing will convince you that the flu shot caused the flu, and you will subsequently tell all your friends and neighbors about it, providing more grist for the rumor mill.

Yet, just because two things happen at about the same time, the first thing to occur does not necessarily cause the latter. That would be akin to proclaiming that stock prices plunged today because the Patriots beat the 49ers yesterday.

Logic dictates that if one could actually get the flu from the flu shot, a much higher percentage of those people getting the flu shot would come down with the flu right away, causing a public relations nightmare far worse than the Tylenol cyanide scandal.

The main reason you cannot get the flu from the flu shot is that the viruses in the shot are inactivated. That means the viruses are dead and cannot spread as a live virus could, just as a dead plant cannot sprout roots. (In contrast, the flu mist or nasal spray vaccine contains a weakened live virus. It will not cause a healthy person to come down with the flu but is not recommended for pregnant women, people with compromised immune systems and other vulnerable populations.)

Even though the flu shot will not cause the flu, you may still experience some short-lived unpleasant side effects, such as low grade fever; body aches; and soreness, swelling or redness at the injection site. A fractional percentage of people will have a more severe allergic reaction to the flu shot called Guillain-Barré syndrome, a condition in which the body's immune system attacks part of the peripheral nervous system. This allergic reaction is actually worse than the flu itself, but it is not the flu.