When you consider that from the time of our birth we are bombarded by millions of potentially disease-causing germs - bacteria, fungi, viruses - that thrive in the world around us, it's amazing that we're not always sick. Even the routine act of eating introduces all kinds of germs into our body. And a bout of strep throat or upper respiratory viral infection multiplies their numbers dramatically.
How do we survive?
We survive because we have an immune system that fights back. It has the capacity to recognize viruses and foreign bacteria, and respond with the creation of special cells called antibodies that tag the invaders so the body's "killer cells" can do their job. This life-saving ability is complemented by the immune system's ability to store the "memory" of the invaders so the next time they appear, our system can respond effectively, thus rendering us immune - to those particular germs, at least. Such naturally acquired immunities allow us to navigate safely much of life's constant stream of colds and other every day illnesses.
How vaccines work
Typically, a vaccine contains small amounts (or parts) of the disease-causing germs, which have been weakened, purified, or killed. The immune system mistakes these duds for the real thing, and creates all the necessary antibodies it needs to fight them. It then stores the information about how to produce these cells for the next assault, which - if it ever comes - is the real thing. Some vaccines bestow a lifelong immunity; others such as the tetanus and pertussis (whooping cough) vaccines require boosters to keep the body's resistance alive.
Different types of vaccines
No vaccine is perfect and so researchers are constantly looking for better ones that cover everyone and are entirely risk free. The vaccines used today belong to one of the categories below:
- Attenuated "live" vaccines: A vaccine with a weakened version of the original disease-causing organism is called attenuated. Because it's so close to the original, it provokes a strong response from the immune system and thus is a very good teacher. Because it's still alive it needs to be refrigerated. In addition, there is an extremely remote possibility that an attenuated germ could - as in the way of all living organisms - mutate and become virulent again. Thus to be absolutely safe, attenuated vaccines are not usually recommended for people with compromised immune systems. Examples: vaccines for measles, mumps, rubella, yellow fever;
- Inactivated or "killed" vaccines: For this type of vaccine, scientists kill the germ either with radiation, heat, or chemicals. Such vaccines can't mutate. They're weaker than attenuated vaccines and thus usually require more than one shot. Examples: vaccines against influenza, hepatitis A, rabies, Japanese encephalitis;
- Subunit vaccines: For this vaccine, scientists keep only the parts of the germ that stimulate the immune system to respond or, as in the case of a recombinant subunit vaccine, they manufacture the important parts of the germ through recombinant DNA technology. Examples: vaccines against hepatitis B, pertussis, pneumonia caused by Streptococcus pneumoniae, haemophilus influenza type b;
- Toxoid vaccines: This type can be used when the illness is caused by a toxin produced by a bacterium. Scientists denature the toxin and use it in the vaccine to teach the immune system to fight off the natural toxin. Examples: vaccines against diphtheria, tetanus.
Vaccines and the rest of us
There is a minimum percentage of the population that needs to be vaccinated in order for all of us to have the benefit of vaccines. This is called herd immunity. There are always some people in a population that don't get vaccinated either because they can't - due to severe allergies or a compromised immune system (e.g., from cancer or from HIV) - or because they won't on personal grounds (usually for religious reasons or because they don't trust the vaccine itself). Normally the herd immunity can cover these exceptions. When the minimum percentage isn't met, however, we begin to see outbreaks of the disease.
Breast-feeding and immunity
Some antibodies are contained in mother's milk, so breast-feeding offers a painless way to pass some disease protection to infants. Breast-feeding, however, does not contain antibodies against all infections. There are many diseases, including diphtheria, polio, tetanus, mumps, pertussis, and measles against which there are only two ways to gain immunity: either get vaccinated or get the disease - with the associated risks.
Currently, we can be immunized against about two dozen different diseases. Vaccines against about half of them (including Japanese encephalitis, yellow fever, and rabies) are only recommended for those who travel to areas in the world where the diseases are constantly present (endemic), usually in Africa or Asia. The remaining vaccines make up the routine immunization program recommended for children living in Canada. Some are given in combination for the sake of convenience and ease of both parent and child, some require a series of shots. Today's standard immunizations for children in Canada include: diphtheria, pertussis, tetanus, poliomyelitis, haemophilus influenza type b bacteria, hepatitis B, measles, mumps, rubella, serogroup C meningitis, pneumococcal disease and varicella (chickenpox).
There are also vaccines to protect against and influenza and HPV. Talk to your health-care provider to find out if these shots are right for your child. These vaccines are given by needle "shots" according to specific schedules that usually start when a baby is two months old.
If you are planning to travel outside of Canada, make sure that you've received the correct immunizations. In addition, vaccinations against such diseases as Japanese encephalitis, typhoid, and yellow fever are often required before travelling to some developing countries.
Costs of vaccines
In Canada, immunizations against the common vaccine-preventable diseases are free of charge. For 5 other recommended vaccines, policies vary across the country, with people in some provinces having to pay up to $300. Canada is working on a national immunization strategy that should bring all provinces in line and add all recommended childhood vaccines to the (free) routine immunization schedule.
Vaccine side effects
After receiving a vaccine injection, there may be tenderness or a slight swelling around the injection spot. Occasionally a person experiences a low fever after an injection. Rarely -in Canada, in the order of one in a million - a person may suffer a severe side effect from a vaccine.
For more information
Ask your doctor or pharmacist about the recommended childhood immunization schedule for your province. Your pharmacist can also provide you with a list of the recommended travel vaccines for your particular destination, as well as refer you to a local travel clinic if needed.