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How Long Does It Take For COVID-19 Vaccine Side Effects to Show?

Cayman Islands Government
Published: April 26 2021
Last Updated: September 10, 2021

The COVID-19 vaccines have been proven to be safe and effective against COVID-19. When you get the vaccine, as with any vaccine, you may experience some mild side effects. 

Side effects are generally your body's way of showing that it is building protection against a disease or virus. But why is it normal to get side effects with vaccines, how do they work, and what's normal for the COVID-19 vaccines?


Why It's Normal To Have Mild Side Effects With Any Vaccine

Vaccines give you the ability to defend yourself against a virus or disease without getting sick with the actual virus.

Often, the symptoms we think of as 'getting sick' are caused by our body's reaction to a virus and not the virus itself. For example, your immune system sometimes raises the temperature of your body to a fever to try and kill off a virus.


How Do Side Effects For Vaccines Work?

So, if the symptoms we associate with the sickness are caused by our immune system, what causes the side effects of a vaccine?

The most common side effects of vaccines, such as muscle aches or a fever, are also caused by our immune system but in this case, it does not mean that we are sick.

Vaccines give our immune systems the information they need to protect the body if a future virus appears.

When you stimulate the immune system with a vaccine, it responds as if you have given it a real, but weaker virus. You haven't received the virus, but it still responds as if you have.

This is why some people get fevers, chills, or aches, or most commonly a sore arm where the injection went in after any vaccine. Often, side effects like this are a sign that your immune response has been triggered, although they are not required to get a good response to a vaccine.


How Long Do Side Effects Last?

Generally, the side effects of vaccines go away in a few days. This is the length of time it takes your immune system to feel satisfied that there actually isn't any threat, so it can relax.


What Are Common COVID-19 Vaccine Side Effects?

With the Pfizer/BioNTech vaccine, some people have experienced aches where the injection went in. Other side effects include:
  • headache
  • muscle aches
  • chills
  • joint pain
  • a raised temperature

More people experience side effects after the second dose than after the first dose. It is typical to experience some kind of side effect, although you will probably find that this is mild and does not impact your day.


What About allergic Reactions?

Side effects are not the same as allergic reactions. Some people may be allergic to some of the ingredients in a vaccine, this can sometimes cause allergic reactions and that is why you are asked to wait 10-15 minutes in the vaccination centre before leaving.

Individuals with a history of anaphylaxis to food, an identified drug or vaccine, or an insect sting can receive any COVID-19 vaccine if they are not known to be allergic to components of the vaccine.  Anaphylaxis is very rare, but the British Society for Allergy and Clinical Immunology (BSACI) has advised that individuals with a history of immediate onset anaphylaxis to multiple classes of drugs or unexplained anaphylaxis should not be vaccinated with the Pfizer/BioNTech vaccine. 


What If I don't Get any Side Effects?

Not having any side effects doesn't mean that the vaccine didn't work.

All bodies, and all people, are different and so all immune systems respond differently to a vaccine. It has been shown that the elderly develop good responses to the Pfizer-BioNTech vaccine even though this group are less likely to have side effects.


More Questions?

Visit our COVID-19 vaccine pages to learn more about the vaccine and how it works.

Remember, side effects after getting a vaccine often means the vaccine is working and your immune system doing what it needs to do. 

Tags: vaccine

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