Can I get influenza from the influenza vaccine?

The influenza vaccine cannot cause influenza (the flu) if you're vaccinated with the inactivated trivalent vaccine, made with killed virus. However, fever and achiness can occur after a flu vaccine. This is not the flu, however, but the result of an activated immune system.

The nasal flu vaccine, which contains a weakened live virus, could, conceivably, cause the flu in someone with a suppressed immune system. Thus, it is only approved for use in healthy people between ages 2 and 49 (younger and older people tend to have weaker immune systems). Studies involving hundreds of healthy children and adults showed no evidence that the nasal flu vaccine resulted in the flu.

However, you can get the flu after being vaccinated if the viral types used to make the vaccine do not match the circulating flu viruses. These viruses change every year, which is why the vaccine changes every year and why you need an annual vaccine. Nonetheless, in any given year the flu vaccine typically protects about 60% of healthy adults under 65. The older you are, the less effective it is, likely because of a weaker immune system.

Even when the vaccine and viruses aren't well matched, the vaccine still protects a considerable number of people. Plus, if you get the flu, having had a vaccine can mean a quicker recovery with fewer complications. And don't forget it takes about two weeks after you're vaccinated before the vaccine fully engages your immune system. During those two weeks, you're still susceptible to an influenza virus, even one the vaccine should protect against.
Patrick Dowling, MD
Family Medicine
The flu vaccine is not a live vaccine. As such, you cannot get influenza, a viral infection, from it. You can get a reaction from a flu shot just like some people get a reaction from certain foods, from touching poison ivy or from being injected by certain substances. This reaction may cause you to feel ill for a couple of days. In contrast, if you really have the flu (not a reaction from the flu shot), you will have fever and chills, hurt all over for 5 days or so, and have congestion. 
You cannot get the flu from the flu vaccine. The flu shot contains inactivated (killed) flu viruses that cannot cause illness. 

Seasonal flu vaccines have a very good safety track record when it comes to side effects. The Centers for Disease Control and Prevention and the Food and Drug Administration closely monitor the safety of seasonal flu vaccines.

Serious problems from inactivated influenza vaccine are very rare. But there is a possibility for some mid side effects, such as soreness, redness, or swelling where the shot was given; red or itchy eyes, cough, aches, headache, fatigue and sometimes fever.
Dr. Elif E. Oker, MD
Medical Toxicology

No, you cannot get the flu from the flu shot as there is no live virus in the vaccine.  

If you experience mild flu like symptoms just after getting the flu shot, this is a sign that your body is building an immune response to the other words the flu shot is working!

So you ask how is it you got the flu the last time you got the vaccine? The answer is likely one of three:

1. You didn't get the flu, but another illness.

2. Your vaccine was not 100% effective. The good news here is that most folks who fall into this category have a milder illness then those who did not get vaccinated.

3. You caught the flu in the period before the vaccine became effective. (It takes 2 weeks for the vaccine to kick in after getting the shot.)

You cannot get influenza (the flu) from the influenza vaccine. Viruses used in the vaccines are either dead or extremely weakened. Some of the side effects of influenza vaccines resemble those of influenza. However, these are not an indication that you have the flu.

A flu shot cannot cause flu illness. The viruses contained in flu shots are inactivated (killed), which means they cannot cause infection.

Flu vaccine manufacturers kill the viruses used in the flu shot during the process of making the vaccine, and batches of flu vaccine are tested to make sure they are safe. In randomized, blinded studies, where some people got flu shots and others got saltwater shots, the only differences in symptoms was increased soreness in the arm and redness at the injection site among people who got the flu shot. There were no differences in terms of body aches, fever, cough, runny nose or sore throat.

The presence of the CDC logo and CDC content on this page should not be construed to imply endorsement by the US Government of any commercial products or services, or to replace the advice of a medical professional. The mark “CDC” is licensed under authority of the PHS.
Diana K. Blythe, MD
Flu shots do not give you the flu, or influenza. What flu shots do is train your body to attack the flu. When your body is shown the flu shot, it creates an immune response which is like your body training for fighting off the flu. You may get a slight elevation in temperature and some pain at the site of injection, but it does not give you the flu.
Check out Dr. Know's explanation about flu shots, which can't really give you the flu. Learn more about influenza in this video from Discovery.

Dr. Mehmet Oz, MD
Cardiology (Cardiovascular Disease)
You know the flu shot can help prevent a nasty case of the flu -- but can it also give you the flu? In this video, Dr. Oz explores this common misconception.

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Vaccines work to protect your body against germs. Because of vaccines, many of the diseases that can cause severe sickness, handicaps and death have been eradicated. Learn more from our experts about vaccines.

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.