Vaccine Safety

Frequently Asked Questions

Previous | FAQ | Next

Are vaccines safe?

Answer: Yes. Vaccines are among the safest tools of modern medicine. Serious side effects are rare. For example, severe allergic reactions can occur, but they very rarely do. In Canada, this kind of reaction has occurred less than once in every 1 million doses of vaccine, and there are effective treatments for this condition. The dangers of vaccine-preventable diseases are many times greater than the risks of a serious adverse reaction to the vaccine. For information on who should not receive specific vaccines, please see the Contraindications and Precautions section of each vaccine chapter in the Canadian Immunization Guide, 7th Edition 2006. Minor side effects from vaccines, on the other hand, are common. Many patients get a mild fever after immunization or soreness where they receive the injection. These reactions are a nuisance but do not usually last long. They can be part of the body's normal response to the vaccine.

No one in the field of public health takes the safety of vaccines for granted. Vaccine safety is an international concern. Information on possible safety concerns is communicated very rapidly among different countries. This careful monitoring ensures that public health authorities can act quickly to address concerns. In addition, research continues to improve vaccines.

Some examples follow:

• In 1999, some babies in the U.S. developed a rare form of bowel obstruction after receiving a new vaccine to prevent rotavirus infection (a cause of diarrhea, sometimes severe, in infants). Pre-licence studies had suggested that there might be an increased risk of this condition, and monitoring effectively picked up the problem. (In the first 1.5 million doses of rotavirus vaccine, 15 cases of bowel obstruction were reported.) Use of this vaccine was stopped in the U.S., and the manufacturer withdrew its request to license the vaccine in Canada.
• The oral polio vaccine (OPV), introduced in the 1950s, prevented hundreds of thousands of polio cases. It was also found to cause a form of paralysis once in every 3 million doses. A vaccine that uses inactivated virus (IPV) is now used almost exclusively throughout the world and cannot cause even this rare adverse event.
• The original whole-cell pertussis (whooping cough) vaccine sometimes caused high fever, seizures or collapse. A vaccine was developed that uses only part of the cell of the pertussis bacterium. This vaccine has fewer side effects and is now used instead.

In considering the safety of vaccines, it is important to look at both risks and benefits. If there were no benefit from a vaccine, even one serious side effect in a million doses could not be justified. If there were no vaccines, however, there would be many more cases of disease, more serious side effects from disease, and more deaths.

The examples from countries that have stopped or decreased their immunization programs have illustrated this fact many times in recent years. The diseases we can prevent with vaccines can lead to pneumonia, deafness, brain damage, heart problems, blindness and paralysis in children who are not protected. We are fortunate in Canada to have vaccines for diseases that still kill and disable children throughout the world every day. The risks of not getting immunized are a lot greater than any risk of immunization itself.

Previous | FAQ | Next