The COVID-19 vaccine, like all vaccines, may cause side effects in some people. Symptoms are usually mild and resolve after a few days. Some of the symptoms are part of the body’s response to developing immunity to a virus.
Clinical trials of Pfizer (external link) and and clinical trials of Moderna (external link) third doses and real world data from Ontario (PDF file) show similar side effects from a third dose of either mRNA vaccine. Data also shows that serious side effects from the booster dose are very rare.
The most commonly reported side effects are:
- pain at the injection site
- swelling, and colour changes in the skin (for example, red, purple) at the injection site
- muscle or joint pain
- mild fever
Ongoing studies on the COVID-19 vaccines have found that serious side effects are extremely rare.
In rare cases, serious allergic reactions (anaphylaxis) can occur. Allergic reactions can be treated and are usually temporary. Contact your doctor if you develop any of the symptoms below. If your symptoms are severe, call 911.
- hives or itchy skin
- swelling of the face or mouth
- trouble breathing or wheezing
- serious drowsiness
- high fever (over 40°C)
- convulsions or seizures
- muscle weakness/ loss of feeling in the face
- chest pain, shortness of breath or excessive sweating
- feeling of a fast, pounding or fluttering heartbeat
- other serious symptoms (for example, “pins and needles” or numbness)
Vaccine side effects will continue to be monitored as people receive the vaccine. If you get a reaction to the vaccine, contact your health care provider who will report the side effect directly to public health. Public health will keep track of the reported side effects to make sure the vaccine continues to be safe.
Learn more about what to expect after vaccination.