You are here

Vaccine side effects

Date last reviewed: 
Tuesday, Mar 12, 2024

On this page:

Vaccines are among the safest medical products available, but like any medicine or supplement (including vitamins), vaccines can cause side effects. Many people who receive vaccines have no side effects at all. For those who do, the side effects are usually minor and only last a day or two. Serious side effects are very rare. 

Did you know?

Because vaccines are given to healthy people, including children, they are held to the highest safety standard—even higher than most drugs used for treatment.

Possible side effects

Side effects are common after getting a vaccine. These can include: 
  • Pain, redness, or swelling where the vaccine was given.
  • Tiredness or headache.
  • Fever and chills.
  • Muscle or joint soreness.
  • Nausea, vomiting, or diarrhea.
  • Fussiness, crying, restlessness, or decreased appetite in infants 
  • After the MMR or chickenpox (varicella) vaccine: fever, rash, or other side effects (including swelling of glands in the cheeks or neck after the MMR vaccine) may occur one to two weeks after immunization.
  • After the nasal spray influenza (flu) vaccine: nasal congestion and runny nose.
An elderly man and woman sitting on a couch while pointing to the band aid on their arm and smiling.
A high fever can happen in infants and young children, especially after the first dose of a vaccine. In a few cases, fever may cause a seizure. A seizure caused by a fever is called a febrile seizure. A febrile seizure is not harmful and usually stops by itself. Febrile seizures can happen with any condition that causes a fever, including common childhood illnesses such as a cold, the flu, an ear infection, or roseola. Learn more about febrile seizures.
Sometimes people faint during or after immunization; this can be common in teens. Fainting is usually triggered by pain or anxiety and can be triggered by many types of medical procedures. Sometimes when people faint, their bodies make jerking movements. These movements can sometimes be confused with seizures but are not actual seizures. Fainting itself is generally not serious, but harm can occur from related falls. Let your health care provider know if you are anxious, have a fear of needles, or have a history of fainting with immunization so that falls can be prevented. You may be able to receive your vaccine lying down.

Have a positive experience.

Find tips for reducing pain and anxiety with immunization in children & teens and adults.

Different vaccines can have different side effects. For vaccine-specific side effects, review the HealthLinkBC Files linked in the immunization schedules.

Rare but serious side effects

Serious side effects from vaccines, including severe allergic reactions, are very rare.  
There is an extremely rare possibility of a person having a life-threatening allergic reaction, called anaphylaxis, after getting a vaccine. True anaphylaxis following immunization occurs at a rate of about 1.3 cases per 1 million doses of vaccine. Symptoms of anaphylaxis may include hives, trouble breathing, or swelling of the throat, tongue, or lips. If left untreated, these reactions can worsen and become life-threatening. Most of these reactions begin within minutes of getting a vaccine. This is why staying at the clinic for 15 minutes after getting any vaccine is important. Anaphylaxis is preventable in many cases and treatable in all. Call 9-1-1 if you or your child have signs of anaphylaxis after leaving the clinic. 
While true anaphylaxis following immunization occurs at a rate of about 1.3 cases per 1 million doses of vaccine, treatment for anaphylaxis at vaccine clinics is started more often (about 1 in 100,000 doses). This is because some people will have milder allergic reactions or have symptoms related to anxiety or feeling faint that can be difficult to tell apart from early anaphylaxis. If a health care provider is concerned these symptoms might be anaphylaxis, they may give adrenaline (also known as epinephrine, as found in ‘epi-pens’) as early treatment is key to a good outcome. Upon later review, most of these events turn out to be due to either a milder allergy or another cause. 
People with a known serious allergy to a vaccine or a vaccine ingredient are not offered that vaccine. Those who experience an event that was thought to be anaphylaxis are often referred to an allergist to help decide if they can get that vaccine again. It is important to remember that vaccines are an uncommon cause of anaphylaxis; far more common causes are food, medications like antibiotics, and insect bites. 
Your health care provider will inform you about potential vaccine side effects before immunization. 

Immunization aftercare sheets

Click the images below to learn what to expect after immunization and how to manage side effects.

Reporting of adverse events

It's important to report any adverse events following immunization (AEFIs) to your immunization provider/clinic or health care provider. Health care providers are trained to report these events to the correct channels to monitor vaccine safety. It is important to report the adverse event even if you don't know if the vaccine caused it. By reporting adverse events, possible vaccine safety concerns can be investigated, and action taken if needed.  
It is important to note that most people who have an adverse event following immunization can safely get immunized again. Your health care provider will tell you what is recommended for you or your child. 

What is an adverse event?

An adverse event following immunization (also known as an AEFI) is any untoward medical occurrence after a vaccine has been given that may or may not have been caused by the vaccine.

Vaccines and health conditions 

Some people have wondered if vaccines can cause conditions such as autism, asthma, and SIDS or autoimmune diseases like diabetes and multiple sclerosis. However, there is no evidence that vaccines cause these conditions. We learn about a vaccine’s safety during clinical trials before it is approved and monitor it continually as millions of doses are administered after its approval. We’ve been monitoring the safety of vaccines for more than 50 years, and the chance a vaccine will cause unanticipated long-term health problems is extremely low.

It's much safer to get the vaccine than the disease 

The risks from the diseases vaccines prevent are much greater than the risk of vaccine side effects. Complications from vaccine-preventable diseases can be severe and life-threatening. 
Some examples: 
  • Chickenpox (varicella) infection can cause pneumonia.
  • Polio infection can cause permanent paralysis.
  • Measles infection can cause encephalitis (swelling of the brain).
  • Mumps infection can cause deafness.
  • Haemophilus influenzae type b (Hib) infection can cause brain damage or even death.
  • Rotavirus infection can cause severe vomiting and diarrhea, which can result in dehydration and hospitalization.
  • Shingles can cause pneumonia (an infection of the lungs), loss of hearing or vision, scarring, nerve pain, and brain inflammation (encephalitis).
People who choose not to get immunized or not to immunize their children often do so to avoid risk, but choosing not to immunize is the riskier choice. 

Canada's vaccine injury support program

‎It is very rare for a vaccine to result in a permanent injury. Canada's Vaccine Injury Support Program (VISP) is a federal program that provides financial support if it is determined that a person has experienced a serious and permanent injury after receiving a Health Canada-approved vaccine, administered in Canada on or after December 8, 2020. This includes all vaccines approved by Health Canada and emergency use authorization vaccines such as COVID-19. Financial support is also available to the dependents of a person who has died after immunization. Learn more about the Vaccine Injury Support Program (VISP).