Disease And Illness - Other
A child in India recieving a polio vaccination

How Vaccines Prevent Disease

A child in India recieving a polio vaccination
Melissa Harber's image for:
"How Vaccines Prevent Disease"
Caption: A child in India recieving a polio vaccination
Image by: Unknown
© Center for Disease Control http://en.wikipedia.org/wiki/File:Vaccination-polio-india.jpg

Most Americans of a certain age remember getting vaccinations at the doctor. These "shots" were usually feared, or at least thought unpleasant by children, who had no idea how they could be helping them stay healthy. Yet vaccines have severely reduced the rates of childhood diseases, such as measles and pertussis, which were once very common, and often led to severe complications or even death. Today, with both growing fears as to vaccination safety and the return of some of these diseases that had not been seen in years, one question is important to understand- how do vaccines prevent these diseases? This question is best explained on two levels.

The first level, is how vaccines prevent an individual person from getting a particular disease. The human body is protected from invading organisms by the immune system. When the immune system fights off a specific microbe, like chicken pox, or measles, the identifying molecules on that microbe, called antigens, are retained by the body so if it is ever infected by the same organism it can be repelled more effectively. This is where the belief that getting a disease such as the measles meant you could never get it again (though this is not entirely true; some diseases such as the cold or flu are caused by many different microbes, or ones that can change themselves to avoid detection). A vaccine works by injecting the person with a weakened or dead form of the disease causing microbe. This allows the person's immune system to copy and create the preventative antigens for that disease, without actually getting sick.

On a larger scale, vaccines prevent disease in a community through what is known as herd immunity. Disease causing germs are passed person to person, through direct contact, body fluids, or through the air. Vaccines are highly effective, but do not fully protect everyone. Additionally, some people with certain illnesses, like leukemia, or are taking medications like corticosteroids which weaken the immune system, cannot receive vaccinations with most others. This can be especially dangerous because vaccine preventable diseases are often far more severe, even life threatening in these populations, and also in infants that are too young to vaccinate. If the as many people who can be vaccinated are, this protects those who are not protected or cannot be vaccinated because no one else is getting the disease and so no one has the germs to pass it to others. However, the more people who opt out of vaccination, the more holes there are in the herd immunity, and the more opportunities there are for these diseases to re-emerge, as has happened recently in some U.S. states with measles and whooping cough. 

More about this author: Melissa Harber

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