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Flu Vaccines Are Safe: Here’s Why

Posted on October 13, 2020
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Flu vaccines help prevent flu-related illness, hospitalizations, and deaths. Flu vaccines have a strong safety record and have been safely administered to hundreds of millions of people over the past 60+ years.

Flu Vaccines Cannot Cause the Flu

If you should happen to feel ill following flu vaccination, there are two common explanations:

  • You may be experiencing side effects of the vaccine, which should not be confused with actually being infected with the flu virus. A slight fever, body aches, or fatigue can be a sign that your immune system is being activated to build immunity in response to the vaccine. This is not flu. When someone is sick with flu, they suffer severe and long-lasting symptoms.
  • Since it can take up to two weeks following flu vaccination for your body to build the proper immune response to help prevent flu, you could have been exposed to the flu virus or a similar virus before you were protected by the vaccine.

Flu vaccines do not contain viruses that can make you sick with the flu. If you are sick after receiving a flu vaccine, it’s likely that you are experiencing an immune response. When you get a flu vaccine, your body learns to fight off a future flu infection by producing antibodies. This process of creating an immune response could make you feel sick for a day or two, but this is good news because it means that your body is gearing up to fight off future flu infections if you become exposed.

Possible Side Effects

Most people who receive the flu vaccine have no reaction. Some people may experience redness and slight swelling at the site of injection, fever, headache, and/or muscle aches. Many of these side effects are actually evidence that your body is responding to the vaccine and preparing to fight off a future flu infection.

Serious side effects, such as Guillain-Barre syndrome, are rare and occur in less than one in one million people who receive a flu vaccine. The risk of rare side effects from vaccination is much lower than the risk of an unvaccinated individual suffering from major flu-related complications should they become ill.

Vaccine Safety Monitoring

The Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) closely monitor the safety of vaccines approved for use in the United States. There are two reporting systems in place that allow for vaccine safety monitoring.

The first is an early warning, self-report system called Vaccine Adverse Event Reporting System (VAERS) that allows anyone to submit a report about side effects and adverse reactions they allegedly experienced following vaccination. However,this system is limited because medical experts do not receive all of the information they need to decide if the vaccine is responsible for that side effect or adverse reaction.

The second system, the Vaccine Safety Datalink (VSD), is a more robust system that includes medical data. These data are collected through a collaboration between CDC and nine healthcare organizations. The VSD conducts vaccine safety studies based on questions and concerns from the medical literature and VAERS reports. This system allows medical experts to track outcomes of people who are vaccinated against influenza to ensure that the vaccine is not causing any unwanted or unexpected side effects.

Additionally, annual flu vaccines go through standard safety testing during manufacturing processes. Vaccines are manufactured in batches called lots and each lot must be tested for safety, purity, and potency according to FDA guidelines before they are released for distribution to the general public.








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