Mission: To save lives and reduce hospitalizations by protecting children, families, and communities against influenza.
Insights on Influenza
  • Flu Facts

FAQs: Does the Flu Vaccine Work?

Posted on January 22, 2021
Share this article:

One common misconception about the flu vaccine is that it doesn’t work – some think that it can even cause the flu! In this post, we’ll answer common questions about the flu shot from our Facebook and Twitter communities.

Does the flu vaccine cause the flu?

No! You cannot contract the flu from a flu vaccine.  Flu vaccines either contain dead (inactivated) or weakened (attenuated) viruses, or even no flu virus at all! The vaccine works by causing your body to create antibodies, basically teaching your body how to fight off the flu. To cause infection, viruses need to reproduce, or make copies of themselves. Flu vaccines, no matter how they are made, do not contain viruses that can reproduce and make you sick with the flu.

Why did I get sick immediately after getting a flu shot? Are the two related?

It might be, but that doesn’t mean you have the flu. Common side effects of flu vaccination can include fever, headache, and/or muscle aches. These common side effects might make you think you are sick, but actually it is proof that your body is having an immune response, which is what it’s supposed to do! Side effects usually last about 1-2 days.

If you did get sick after getting vaccinated, keep in mind it takes about two weeks following vaccination for your immune system to build up enough antibodies to be immune to the flu. You might have been exposed to the virus before or immediately after you received your vaccine and started showing symptoms later on. It is impossible to get the flu from a flu vaccine.

It is also possible that you are sick with another virus going around, such as the common cold.

I got my flu shot, but I still got sick. Why didn’t the vaccine work?

The flu vaccine is not a 100% guarantee that you will not get the flu because each year there are different circulating strains of the flu virus. However, the vaccine can still protect you even if it’s not a perfect match to circulating flu strains. Studies show not only can the flu vaccine prevent illness, more importantly the flu vaccine also reduces the severity of flu-related complications such as hospitalizations and death. This means if you get your vaccine and still get sick, you might not be sick for as long or have as serious of an illness – and more importantly, you’re less likely to become hospitalized or die if you’re vaccinated.

You might also be interested in...

Spot the Fake: Identifying and Comparing Good vs Bad Articles
History of Vaccines: How and Why Do Vaccines Work
Prevent winter flu with these tips.
7 Ways to Keep Your Family Healthy this Winter
Stay Informed
Sign up for our Weekly Flu News and quarterly newsletter, Fighting Influenza, to stay up-to-date on the latest flu news.


You are required to accept all of the terms and conditions in this License Agreement in order to receive a limited, non-exclusive, non-transferable, non-assignable, royalty-free license to use the FAMILIES FIGHTING FLU, INC. logo, displayed below (the “FFF Logo”), from Families Fighting Flu, Inc. (“FFF”). In order to accept these terms and conditions, you must click the “I Accept” button below.

  1. FFF hereby grants to you, and you accept, a limited, non-exclusive, non-transferable, non-assignable, royalty-free license to use the FFF Logo, which you may download and use solely in online and print earned media publications for a period of no more than six (6) months in the United States.
  2. You acknowledge that the FFF Logo is a valid trademark; that FFF is the sole owner of the FFF Logo; and that FFF retains all right, title, and interest in and to the FFF Logo. You agree that any and all use that you make of the FFF Logo, and any and all goodwill arising from your use of the FFF Logo, shall inure exclusively to the benefit of FFF.  You also agree that you shall not challenge the validity of the FFF Logo or FFF’s ownership or title thereto during the term of the License Agreement or thereafter.
  3. You agree that you shall use the FFF Logo only in the form shown above, and that you shall not alter, modify, change, or edit the FFF Logo in any manner.
  4. You acknowledge the valuable goodwill and reputation in the FFF Logo, and that it is essential that the high standards and reputation associated with the FFF Logo be maintained. You therefore agree to use the FFF Logo consistent with the highest standards of quality so as to protect and maintain the FFF Logo and FFF’s rights therein.
  5. FFF shall have the right to review and inspect your use of the FFF Logo at any time. FFF, in its sole discretion, may determine that you are not using the FFF Logo in an acceptable manner and require that you discontinue your use of the FFF Logo.  To the extent that FFF requires that you discontinue your use of the FFF Logo, you agree that you shall remove the FFF Logo from all online and print earned media publications as soon as practicable under the circumstances, and that you shall not use the FFF at any time in the future.
  6. You must include the following notice in connection with any use of the FFF Logo: “The Families Fighting Flu, Inc. logo is the registered trademark of Families Fighting Flu, Inc.”
I Accept