Why the Flu Shot Didn't Give You the Flu

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Millions of people get flu vaccines every year to protect themselves and those around them from the flu. Yet millions of others don't simply because they believe one of many myths about the vaccine.

One of the most commonly circulated myths that people refer to when refusing the vaccine is that they or someone they know got the flu from the flu shot in the past.

It can be hard to convince someone otherwise when they believe the flu shot gave them the flu, but we'll do our best to explain why it can't happen.

The Science

It is scientifically and medically impossible to get the flu from a flu shot. The flu vaccine contains a dead virus and a dead virus can't make you sick.

If you got the nasal spray flu vaccine, it contains a weakened live virus which, although it is technically not dead, has been inactivated so that it cannot make you sick.

What Could Have Happened

So if science says it's impossible that the vaccine gave you the flu, what happened? There are several possibilities.

  1. If you truly got the flu (not just symptoms that you assumed were the flu) you were most likely exposed to it before you got the vaccine or during the two weeks after you were vaccinated. Because the flu vaccine takes two weeks before it has time to take effect and provide you with immunity, you can still get the flu during that time.
  2. You got a strain of flu that wasn't included in the vaccine. Flu vaccines contain the three (or four) strains of influenza that researchers believe are most likely to cause illness the following flu season. But they sometimes get it wrong or there may be multiple strains of flu circulating, not all of which were in the vaccine you got.
  3. You had an illness that was very similar to the flu but it wasn't actually caused by the influenza virus. These illnesses are often referred to as influenza like illnesses (ILI) in the medical community because the symptoms closely resemble flu symptoms but are caused by different viruses.

Before you go around blaming the flu shot for making you sick, make you sure you know what the flu is and isn't.

In simpler terms, just because you got sick after the flu shot doesn't mean it gave you the flu. Many studies have been conducted on the safety and efficacy of flu vaccines and the evidence is clear—flu shots can't give you the flu.

On rare occasions, vaccines, like any other medication or device can cause serious adverse reactions. If you believe a flu vaccine caused serious injury, you or your health care provider can report it through the Vaccine Adverse Event Reporting System. However, getting the flu or a flu-like illness after getting a flu shot would not count as an adverse event.

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