What “safe” means
Recommended vaccines have benefits that outweigh their known risks for the people they are recommended for. This does not mean zero risk or a guarantee that illness cannot occur. The balance varies with the infection, vaccine, age and health history.
After a vaccine: what to watch for
Soreness, tiredness, fussiness or fever can happen. Some live vaccines cause a fever or rash later, rather than the next day. Read the vaccine-specific page and follow the clinic’s aftercare instructions.
Call 911 for trouble breathing or swelling of the tongue or throat. Not sure whether a reaction is expected? Contact a healthcare provider or call 811 for advice. Seek care promptly if symptoms are worrying or getting worse.
A baby under 3 months with a fever needs urgent assessment; babies under 6 months with a fever should see a healthcare provider. Do not assume the fever is a vaccine reaction.
Ask a provider or pharmacist about age- and weight-appropriate pain or fever medicine. Do not give aspirin to a child unless it has been prescribed. Tell a provider or public health unit about a serious or unexpected event after vaccination.
Before the appointment
- Mention a serious previous reaction or a known allergy to a vaccine ingredient.
- Discuss immune-system conditions and pregnancy. Also mention medicines that weaken immunity and recent blood products or immune globulin (an antibody treatment). Some live vaccines need different precautions or timing.
- A mild cold often does not require delaying a vaccine. The vaccinator should assess the child on the day.
- Ask about comfort measures: breastfeeding, distraction, supportive positioning or a numbing cream. Tell the clinic about needle fear or fainting.
What is in a vaccine?
Vaccine ingredients have different jobs. The active ingredient teaches the immune system what to recognize. Other ingredients may strengthen the response, keep the vaccine stable or prevent contamination. Small traces from manufacturing may remain. Ingredient guidance
The specific substance, amount and way it is given matter. Familiarity or a comparison with food is not enough to assess safety or allergies. Different brands and formulations can have different ingredients and packaging.
For an allergy check, use the exact product’s official information (product monograph) with a provider. A general ingredient list cannot confirm whether a vaccine is suitable.
Health Canada — Drug Product Database and product monographs
How safety is monitored
Health Canada reviews evidence before authorizing a vaccine. Safety monitoring continues afterward to look for rare or unexpected problems. An adverse event following immunization means an event happened after a dose; it does not, by itself, prove the vaccine caused it. Reports are assessed for patterns and possible causes.
Sources and references (6)
- Canadian Immunization Guide — vaccine safety and monitoring
- Canadian Immunization Guide — vaccine ingredients
- Health Canada — Drug Product Database and product monographs
- Ontario — tips for a more comfortable vaccine visit
- Canadian Paediatric Society — fever and temperature taking
- Canadian Immunization Guide — precautions and contraindications
Program details can change. How this guide is reviewed