Information
November 2002
Questions and Answers about Vaccination
1. Do vaccines work?
Yes. They are so effective that most of the diseases they prevent are rare in Canada.
Some people do not develop full immunity after being vaccinated so some immunization programs include
a second or third dose of the vaccine. For some diseases, we need booster doses because the protection
wears off over time. No vaccine will work for 100 per cent of the people who receive it.
2. Are vaccines safe?
Yes. Vaccines are among the safest tools of modern medicine. Serious side effects are rare. For
example, severe allergic reactions can occur, but they are rare. In Canada, severe allergic reactions
occurred less than once in every one million doses of vaccine. The dangers of vaccine-preventable
diseases are far greater than the risks of serious adverse reaction to the vaccine.
3. How are vaccines made and licensed in Canada?
In Canada, vaccines for humans are regulated by the Biologics and Genetic Therapeutics Directorate
of Health Canada. They must undergo several stages of rigorous testing before they are approved for
use. The Directorate also supervises all aspects of vaccine production by the manufacturers. Before
any vaccine is licensed and approved for use in Canada, the factory where it is manufactured must
be inspected to ensure that all stages of production meet the requirements for safety, sterility
and quality control. Before release, each vaccine batch is tested for safety and quality under guidelines
specified by the Biologics and Radio Pharmaceuticals Evaluation Centre.
4. What would happen if we stopped immunizing?
Experiences in other countries show that diseases quickly return when fewer people are immunized:
- In Ireland, measles cases soared to more than 1,200 in 2000, as compared with 148 the previous
year, because immunization rates fell to about 76 per cent. Several children died in this outbreak.
- A rubella outbreak occurred in Nebraska in 1999 and all 83 cases involved adults who had not
been immunized. Most of the adults came from countries where rubella immunization is not routine.
- In 1994, there were 5,000 deaths from diphtheria in Russia after the organized immunization system
was suspended.
- In the United Kingdom, a major drop in immunization rates against pertussis (whooping cough)
in 1974 was followed by an epidemic of more than 100,000 cases and 38 deaths in 1978.
5. Why do we still need vaccines if the diseases they prevent have disappeared from our part of
the world?
It's important to continue vaccine programs for four basic reasons:
- First, unless a disease has completely disappeared, there is a real risk that small outbreaks
can turn into large epidemics if most of the community is not protected. So far, the only disease
that has been eradicated from the world is smallpox.
- Second, no vaccine is 100 per cent effective. There will always be some people who will not develop
immunity, even though they have had their shots. This small minority will be protected as long
as people around them are immunized.
- Third, there are a small number of people who cannot receive vaccines. These may be people who
have previously had a severe allergic reaction to a component of the vaccine, or they have a medical
condition that makes receiving vaccines too risky for them. These people are not protected from
disease, and for some diseases it is very important that people around them are immune and cannot
pass disease along to them. By protecting themselves, immunized people can also protect those around
them who are vulnerable to disease.
- Fourth, most vaccine-preventable diseases are still common in other parts of the world. Travellers
can carry them from country to country. If we are not protected by immunization, these diseases
will quickly spread.
6. Won't breastfeeding and good nutrition prevent these childhood infections?
Breastfeeding is not an alternative to infant vaccination, and it does not enhance the responses
to vaccination. Breastfeeding provides some protection against many infections because special antibodies
are made in the breast and are present in human breast milk. Babies who are breastfed generally have
lower rates of many infections, including viral respiratory infections, ear infections and diarrhea.
The protection provided by breast milk is incomplete and can be overcome if the baby is exposed to
a large amount of a germ. Moreover, the protection disappears rapidly as soon as breastfeeding stops.
Good nutrition helps the body's defences against infection to function normally. Infections are
more severe in anyone with poor nutrition. For this reason, malnourished children are much more likely
to die of infections such as measles or pertussis than well-nourished children. Vitamin A deficiency,
in particular, greatly increases the risk of severe illness.
7. Can mercury in vaccines cause brain damage, retardation, autism, attention deficit disorder,
learning disorders?
Mercury was present in some vaccines in the form of thimerosal. Thimerosal is an organic mercury
compound which has been used as a preservative in some vaccines and other medications since the 1930s.
Thimerosal is not methyl mercury. Methyl mercury is a different compound which is known to cause
brain damage.
Thimerosal is used to prevent the growth of bacteria and fungi in multidose vials of vaccines. If
such contamination occurred, it could cause serious infections in people getting the vaccine. Thimerosal
is also used as an inactivating or antibacterial agent in the manufacturing process for some vaccines.
Such use contributes little to the final concentration of thimerosal in vaccines.
There is no evidence that the presence of thimerasol in vaccines given appropriately has caused
brain damage in any child. Newer production methods and availability of alternative preservatives
have resulted in the discontinuation of use of thimerasol in vaccines in North America.
As of March 2001, all vaccines for routine immunization of children in USA and Canada are
available without thimerosal.
8. Don't infections like measles stimulate the immune system and lead to better overall health?
There is no scientific evidence that infection with measles or any other germ is necessary or important
for natural and healthy development of the immune system. In fact, what we know of measles makes
it extremely unlikely that measles plays any role whatsoever in the normal development of the human
immune system.
Natural infection with measles does not provide a general form of stimulation of the immune system.
It stimulates immunity to measles only. In fact, measles infection results in marked suppression
of many parts of the immune system, which lasts for several months. During this time, the child is
more susceptible to a number of other infections. This suppression of the immune system caused by
measles actually leads to the high rate of other infections that complicate measles.
9. Don't some vaccines contain brain tissue, which can cause mad cow disease?
No. The only vaccine that once contained brain tissue was the original rabies vaccine, which contained
rabbit brain tissue. That vaccine is no longer used in Canada or the United States.
10. Do vaccines contain blood, serum, animal tissue or fetal tissue?
No vaccine contains human blood or serum. Trace amounts of human albumin (a protein fractionated
from whole blood) are used as a stabilizer in rabies vaccine and other vaccines. No vaccine contains
animal or human cells.
11. Can vaccines "wear out" the immune system?
The human immune system has a truly enormous capacity to recognize different proteins and other
chemicals called antigens. It can respond to intense and repeated stimulation. The challenge that
vaccination presents to the immune system is not likely to be a significant addition to the daily
load of foreign antigens entering the body, even for a 2-month-old baby. Scientists have estimated
that infants have the capacity to respond to about 10,000 different antigens at any one time. The
vaccines used today are much more highly purified than those in the past so that even though infants
and children now receive more vaccines than they did 30 years ago, the total amount of proteins and
polysaccharides is much lower today than it used to be.
12. Can measles vaccine or MMR vaccine cause autism or other kinds of brain damage?
In 1998, a British physician named Dr. Andrew Wakefield described 12 children whom he claimed had
a new and unique form of bowel disease. Most of the children also were said to have autism, although
that diagnosis was not confirmed. Dr. Wakefield claimed that symptoms of autism in these children
developed soon after immunization with MMR vaccine. Dr. Wakefield proposed the following theory in
which he linked measles vaccine and autism:
- MMR vaccine may produce damage to the bowel;
- The bowel damage leads to either
- impaired absorption of vitamins or micronutrients, or
- an increase in intestinal permeability to protein,
- Either state leads to the formation of antibodies (antibodies that attack tissues in the body)
that damage the brain.
There is NO scientific evidence to support Dr. Wakefield's theory.
Excerpts from:
Your Child's Best Shot: A parent's guide to vaccination (2nd edition),
published by the Canadian Paediatric Society, 2002
Canada's National Immunization Guide (6th edition), published by Health Canada, 2002
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