What is vaccination?

When you introduce a microbe (a bacterium or virus) into the bloodstream, that amazing network of cells that we call the IMMUNE SYSTEM searches them out and tries to destroy them. This is because it has the ability to tell the difference between something foreign, like a bacteria, and cells that belong to our bodies. Many microbes are so tricky that it is really hard for our bodies to fight the infection....and we get sick. The virus that causes the common cold is one of the trickiest! Why? For many bacteria and viruses, if we are exposed to them often enough, our body builds up an IMMUNITY. This means that our immune system has been trained so well to fight off a disease, that the bacteria are killed off before they can make us sick. By injecting someone with either a "little part" of a microbe or a microbe that has been heat killed (vaccination), we are training the immune system to be an expert at recognizing and killing off that invader.

How does the Immune System work?

Flash Interactive Game available on Home Page....

Did you know?....

If levels of vaccination decrease, many of the (currently) more rare diseases can come back as serious human threats...since many viruses and bacteria have the ability to "hide out" in other animals and be passed between these animals and humans.

A note about adult vaccination....even if you were vaccinated as a child, it is often recommended to update certain vaccinations (ESPECIALLY if you will be doing any international travelling). See this CDC site for more info. In addition, it is a good idea to check CDC recommendations when travelling to more exotic places. It may be suggested that you get vaccinated against certain diseases (such as yellow fever or hepatitis) or that you take anti-malaria drugs to prevent getting the disease. Some vaccinations require 3 shots over a 6 month period, so try to think ahead!


Information on Vaccine Shortages (United States 2004), in particular, 3rd and 4th dose of Pneumococcus (Prevnar) vaccine may need to be delayed. See here.
Adverse events associated with 17D-derived Yellow Fever Vaccination (United States, 2001-2002)
Danish study finds no link between thimerosal and autism

March 2004 - 10 of the 13 original authors of a 1998 study linking the MMR vaccine to a type of autism have retracted their conclusions

U.S. Institute Of Medicine finds no evidence linking MMR vaccine and thimerosal to autism - Infectious Diseases in Children article

Safety Issues

Can a vaccine actually cause the disease it is meant to prevent?

  • This depends on the way that the vaccine is prepared. If it is a LIVE vaccine, there can be a miniscule risk. For instance, with the live oral polio vaccine you had a 1 in 4,000,000 chance of contracting polio from the vaccine. But the risk of getting polio from the environment was so much higher that it was much wiser to get vaccinated. Nowadays, there is no risk from the injectable form of the polio vaccine. Certain vaccines given today are made with live virus (e.g. MMR & Chicken pox), but the virus is altered (attenuated) so that it cannot cause infection. In general, "live, attenuated" vaccines are much more effective in boosting immunity (and the immunity lasts longer) than vaccines made with killed bacteria or parts of bacteria (e.g. toxoid).

  • Evaluating Vaccine Safety Information

  • With any website (including mine!) I urge caution.
  • Suggestions to parents searching for vaccine safety information on the web (Taken from Update : Vaccine-Preventable Diseases (Canada) Vol 6 No 3 July 1999 and WHO site)

    If you decide NOT to have your child vaccinated...

    While I personally believe in having my children vaccinated, I realize that some parents have very strong personal or religious reasons for not wanting their children vaccinated. Additionally, in rare instances, a parent or other family member may have had a severe reaction to a particular vaccine and may be counselled against having their child receive this vaccine (as allergies and severe reactions may be hereditary). In this case, it is strongly recommended to:

    1. limit your child's contact with pregnant women, as certain diseases like measles, rubella and chicken pox can cause miscarriages or birth defects;
    2. keep a close eye on your local public health situation (in order to keep your child away from any possible outbreaks of diseases that s/he is not vaccinated against);
    3. be very careful of any wounds as the bacteria that causes tetanus are found VERY commonly in dirt. Tetanus can be life threatening!

  • Bibliography

    Harvard Med School Parent Issues includes some articles on vaccination
    Excellent primer on vaccines from Children's Hospital of Philadelphia
    United Kingdom NHS immunization homepage
    Excellent article on the "Is vaccination safe" debate (pdf file)
    6 common misconceptions about vaccination
    Funny and comprehensive article about vaccination from a pediatrician's perspective






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