Canadian Immunization Guide 2006
Canadian Immunization Guide
Seventh Edition - 2006
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Part 1
General Guidelines
General
Considerations
The goal of those concerned with
immunization is the elimination of vaccine-preventable diseases.
Eradication of smallpox has been achieved. Currently, global
efforts are directed at the eradication of polio and the
elimination of measles. Ongoing immunization programs with high
vaccine coverage are needed to maintain low levels of other
vaccine-preventable diseases. When the incidence of a
communicable disease decreases to low levels because of
successful vaccination programs, there is a potential for people
to question the need to continue the programs, and this may lead
to lower vaccine coverage and, inevitably, resurgence of the
disease. Therefore, immunization providers must advocate for the
continuation of successful programs.
An ideal vaccine would confer lifelong
protection against a disease after a single dose. It would be
inexpensive, stable during shipping and storage, easy to
administer and without adverse effects. Researchers and vaccine
manufacturers continue to work to improve vaccines; in the
meantime, our existing vaccines save lives. The diseases against
which vaccines protect may also change over time for reasons
unrelated to vaccine programs.
These factors mean that the efficacy,
effectiveness and safety of vaccines and vaccination programs
must be evaluated continually to ensure that
Canadians achieve the greatest possible
benefit.
In this Guide, information
is presented on the immunizing agents available in Canada and
their use in the prevention of communicable diseases. Recommendations on routine immunizations
are discussed in some detail, and an attempt is made to answer
most of the day-to-day queries from providers regarding
immunization.
Because of variation in
manufacturers' products, precise details of the dosage and
route of administration of individual products are not usually
given. Readers are referred to manufacturers' labelling and
package inserts for this information. As well, the manufacturer
has sought approval of the vaccine and provided evidence as to
its safety and efficacy only when it is used in accordance with
the product monograph. Some information in the Guide may differ from that in product monograph(s) and
package inserts.
Information in the Guide is based upon
the best and most current publicly available scientific
knowledge.
What's in a
vaccine?
Vaccines are highly regulated, complex
biologic products designed to induce a protective immune response
both effectively and safely. The main vaccine types as well as
the derivation, purpose and potential risk of vaccine
constituents are summarized below. See Table 1 for
specific information on the type and key constituents of each
vaccine marketed in Canada.
Immunogen: The part of the vaccine that stimulates an immune
response is also the basis for classification of vaccine type, as
follows:
-
Live attenuated: The vaccine contains whole, living bacteria
or viruses that induce immunity by actively replicating within
the host. Since the agent replicates within the recipient, the
stimulus more closely resembles that associated with natural
infection, resulting in longer lasting and broader immunity than
can be achieved with other vaccine types.
Attenuated means the vaccine strains are
weakened so that infection is usually inapparent or very mild, in
marked contrast to the natural infection (see inside back cover).
Live vaccines require careful storage and handling to avoid
inadvertent inactivation and are contraindicated for pregnant
women and people with immunodeficiencies.
Inactivated: The vaccine contains killed bacteria or virus. Such
vaccines pose no risk for immunocompromised persons and may
induce a broad immunity since multiple antigens are present.
Disadvantages include the usual need for multiple doses because
the response may be weaker than that induced by live organisms
and potential toxicity associated with unwanted portions of the
killed organism (as was true for the whole-cell pertussis
vaccine).
Subunit: The vaccine contains purified products that usually
come from the bacteria or virus that causes natural infection but
may also be synthesized in the laboratory using recombinant
technology (e.g., hepatitis
B surface antigen). These products may
require inactivation to prevent toxic side effects, and all are
purified through a variety of steps in the manufacturing
process. The end products include proteins, polysaccharides and
protein-polysaccharide conjugates. Subunit vaccines have
excellent safety profiles and facilitate the preparation of a
variety of combination products. Disadvantages include lower
immunogenicity, which sometimes requires the presence of an
adjuvant and/or multiple doses.
Adjuvant: A substance added to a vaccine to enhance the immune
response by degree and/or duration, making it possible to reduce
the amount of immunogen per dose or the total number of doses
needed to achieve immunity. The only adjuvants used in vaccines
currently marketed in Canada are aluminum salts (aluminum
hydroxide, aluminum phosphate or potassium aluminum sulfate),
which primarily enhance the immune response to proteins. They
have been shown to be safe over seven decades of use. Rarely,
they may cause injection site reactions, including subcutaneous
nodules, granulomatous inflammation or contact hypersensitivity.
Subcutaneous rather than intramuscular deposition, as occurs when
using too short a needle, may increase the risk of such
reactions. After oxygen and silicon, aluminum is the third most
abundant element in the environment and daily exposure occurs,
primarily through food. Infant formula contains from 0.2 to 1.1
mg aluminum/litre whereas vaccines contain from 0.2 to 0.85 mg
per dose. Both exposures are considered to be within the limits
of safety (see Keith et al. for a more detailed
discussion).
Preservatives: Chemicals (e.g., thimerosal, phenol, 2
phenoxyethanol) added to multidose, killed or subunit vaccines in
order to prevent serious secondary infections as a result of
bacterial or fungal contamination. In recent years there has been
a great deal of opposition to the use of thimerosal, an ethyl
mercury derivative, because of a theoretical risk of brain
damage. Scientific evidence has refuted this risk, and it is no
longer necessary for health care providers to raise this as a
concern before administering influenza or hepatitis B vaccines,
which may contain thimerosal. Thimerosal-free versions of both
vaccines are available for use in select circumstances (see the
relevant chapters in this Guide ).
Additives: Substances other than those already mentioned may be
added to vaccines for two different purposes:
- to support the growth and purification of specific immunogens and/or the inactivation of
toxins. These include
antibiotics added to prevent contamination during viral cell
culture; substances needed for the growth of viruses, such as egg
or yeast proteins, glycerol, serum, amino acids and enzymes; and
formaldehyde used to inactivate viruses and protein toxins. Most
of these reagents are removed in subsequent manufacturing steps,
but minute "trace" amounts may remain in the final
product. The amounts present are only of consequence for
individuals who are allergic to them (see Table 1 for a listing
of potential allergens in vaccines authorized for marketing in
Canada). Concern has been expressed about formaldehyde because of
its use as an embalming agent. However formaldehyde is also an
intermediate in human metabolism, and the amount normally found
in blood, even of a young infant, exceeds by 10 fold or more what
is found in a dose of vaccine.
- to confirm product quality or
stability. Compounds may be
added to vaccines for a variety of manufacture-related issues:
controlling acidity
(pH); stabilizing immunogens through
necessary steps in the manufacturing process, such as freeze
drying; and preventing immunogens from adhering to the sides of
glass vials with a resultant loss in immunogenicity. Examples of
such additives include potassium or sodium salts, lactose,
polysorbate 20 or 80, human serum albumin and a variety of animal
proteins, such as gelatin and bovine serum albumin. Concerns have
been expressed regarding the following:
- Human serum albumin: There is a
theoretical risk of infectious agents being present in products
made from human blood. However, steps in the manufacturing
process of both human albumin and vaccines that contain it
greatly reduce the possibility of transmission of these agents.
To date, there have been no documented cases of transmission of
infectious agents by human serum albumin.
- Gelatin: This protein may be the cause
of rare hypersensitivity reactions to gelatin-containing vaccines
(approximately 1 event per 2 million doses). Table 1 identifies
which of the vaccines currently marketed in Canada contain
gelatin. All individuals who have had an
anaphylactic reaction to one of these
products should be referred to an allergist, as should
individuals with a history of immediate allergic reactions to
foods containing gelatin.
- Bovine reagents: The risk of
transmitting variant Creutzfeld Jakob disease from vaccines
containing bovine-derived material is theoretical, estimated to
be 1 in 40 billion or less (see http://www.fda.gov/cber/BSE/risk.htm). In Canada, the bovine-derived reagents
commonly added to vaccines included in the routine schedule are
manufactured from animals considered to be free of bovine
spongiform encephalopathy.
Table 1. Type and Contents of
Vaccines Currently Approved for Use in Canada (May 2006)
Selected references
Keith LS, Jones DE, Chou C. Aluminum toxicokinetics regarding infant
diet and vaccinations.
Vaccine 2002;20:S13-17.
Offit PA, Jew RK. Addressing parents' concerns: Do vaccines
contain harmful preservatives, adjuvants, additives, or
residuals? Pediatrics
2003;112:1394-1397. URL: <www.pediatrics.org/cgi/content/full/112/6/1394>.
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