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FAQs: Does the Flu Vaccine Work?

FFF FAQ
Posted on January 22, 2021

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.

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