Side effects

Did you know?

Vaccines are among the safest tools of modern medicine. Because vaccines are given to healthy people, these products are held to the highest standards of safety. 

Vaccines are among the safest medical products available, but like any medicine, they can cause side effects. 

Before getting a vaccine, your health care provider will tell you about the possible side effects of the vaccine. It’s important to be open with your health care provider and ask any questions you may have.

Most vaccine side effects are minor and only last a day or two.

Many people who receive vaccines have no side effects. For those that do, the side effects are usually very minor, like soreness, redness, or swelling where the vaccine was given, or a mild fever. These effects will generally subside after a day or two. Some side effects are from the process of immunization, such as those related to fear of getting a needle (for example, anxiety with hyperventilation or fainting).  

Serious side effects are very rare.

Some people might have a more serious reaction to a vaccine, like a high fever. Sometimes a high fever (which can be caused by many common childhood infections) can cause a seizure, called a febrile seizure. Febrile seizures which happen more commonly in infants and young children, look serious, but almost never are, and children recover with no lasting effects. Children who have a febrile seizure after getting a vaccine are also more likely to have a febrile seizure if they have a fever for another reason, such as a viral or bacterial infection.

Very rarely, a person will have a true serious reaction to a vaccine, like a severe allergic reaction (called anaphylaxis). The chance of this occurring is between one in 100,000 and one in a million. Just in case, you will always be asked to wait 15 minutes after receiving a vaccine before leaving. If this reaction occurs, health care providers are trained to recognize and treat it.

It is often hard to tell if a reaction was caused by the vaccine or if it was caused by something else.

It is often hard to tell if a reaction was caused by the vaccine, or if it was caused by something else. For example, if you get hives (an allergic reaction) right after a vaccination, it's more likely to be caused by the vaccine than if you get them the next day. 

Rare events, such as Guillain-Barre syndrome (GBS), a form of paralysis that usually resolves, are thought to be associated with some vaccines such as influenza and perhaps with tetanus. These events may occur in about one in a million people who receive the vaccine.  Most of these events occur following infections with viruses or bacteria, and not following vaccines. For instance, the risk of GBS after influenza infection is about 17 times higher than it is after influenza vaccination. The vaccine is still safer than the risk of disease.

Where can you find more information on side effects?

During the immunization visit, your health care provider will review with you the common reactions to each vaccine and will advise that you seek medical attention if you or your child experiences a serious or unexpected reaction.

You can also find a list of possible reactions to each vaccine online in the vaccine’s HealthLinkBC File.  B.C.’s routine immunization schedules with links to the HealthLinkBC Files can be found here.

Concerned about a vaccine reaction?

If you are concerned about any reactions or worried at all about your child, call your doctor, community health centre or HealthLinkBC at 8-1-1. If it is an emergency, call 9-1-1. 

What if your child has a reaction to a vaccine?

Common vaccine reactions (such as soreness, redness, and swelling in the leg or arm where the vaccine was given, or a low fever) may make your child uncomfortable, but these are not harmful. They will generally subside in a day or two.

For a fever in an infant or young child:

  • Let your child breastfeed more, or offer more to drink.
  • Take off extra clothes that your child is wearing.
  • Give your child medicine to help bring down the fever and make them more comfortable. Learn more (pages 16-17).

If your child cries more than normal or has soreness in the arm or leg where the vaccine was given:

  • Cuddle your child to soothe them.
  • Put a cool cloth on the arm or leg where your child got the vaccine.
  • Give your child medicine to help make them comfortable. Learn more (pages 16-17).

What is an adverse event?

An adverse event following immunization (also known as an AEFI) is a serious or unexpected reaction that happens after someone receives a vaccine. An adverse event may or may not have been caused by the vaccine.

It is important to report any unexpected or serious reactions (called adverse events) to your health care provider so that they can be investigated further. It is important to report the adverse event even if you don’t know if it was caused by the vaccine. By reporting adverse events, possible vaccine safety concerns can be investigated and appropriate actions taken.

It is important to note that most children who have an adverse event following immunization can safely get immunized again. Your health care provider will tell you what is recommended for your child.

Learn more about vaccine safety monitoring and adverse events here

Choosing not to immunize is the riskier choice.

Some people choose not to immunize because they’re worried about the risk of possible side effects. But choosing not to immunize is the riskier choice. The risks from the diseases vaccines prevent are much greater than the risk of a vaccine side effect. If you choose not to immunize your child, it’s important to understand the risks and to know how to reduce the risk of your child getting a disease and spreading it to others. Learn more.