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How Vaccines Work
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Vaccine Basics

How Vaccines Work

What is Immunity?
When disease germs enter your body, they start to reproduce. Your immune system recognizes these germs as foreign invaders and responds by making proteins called antibodies. These antibodies’ first job is to help destroy the germs that are making you sick. They can’t act fast enough to prevent you from becoming sick, but by eliminating the attacking germs, antibodies help you to get well.
The antibodies’ second job is to protect you from future infections. They remain in your bloodstream, and if the same germs ever try to infect you again — even after many years — they will come to your defense. Only now that they are experienced at fighting these particular germs, they can destroy them before they have a chance to make you sick. This is immunity. It is why most people get diseases like measles or chickenpox only once, even though they might be exposed many times during their lifetime.
 
Vaccines to the Rescue
Vaccines offer a solution to this problem. They help you develop immunity without getting sick first.
Vaccines are made from the same germs (or parts of them) that cause disease; for example, polio vaccine is made from polio virus. But the germs in vaccines are either killed or weakened so they won’t make you sick.
Vaccines containing these weakened or killed germs are introduced into your body, usually by injection. Your immune system reacts to the vaccine the same as it would if it were being invaded by the disease — by making antibodies. The antibodies destroy the vaccine germs just as they would the disease germs — like a training exercise. Then they stay in your body, giving you immunity. If you are ever exposed to the real disease, the antibodies are there to protect you.
Source: Centers for Disease Control and Prevention, How Vaccines Prevent Disease
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Video Library
Video: How a Vaccine Works
How a Vaccine Works: Ever wonder what exactly a vaccine does to prevent you from getting sick? Watch this video to find out how it works.
>> view all vaccine basics videos
More Information
Understanding How Vaccines Work
Understanding How Vaccines Work
More in-depth information on how vaccines prevent disease
How Vaccines Work — History of Vaccines
How Vaccines Work — History of Vaccines
Learn about the human immune system's response to vaccination
How Do Vaccines Work?
How Do Vaccines Work?
The story of Chip and Dale from the Vaccine Education Center 
 
Content reviewed on October 9, 2013
Immunization Action Coalition  •  1573 Selby Avenue, Suite 234  •  Saint Paul, MN 55104
tel 651-647-9009  •  fax 651-647-9131
 
The Immunization Action Coalition (IAC), a non-profit organization, works to increase immunization rates and prevent disease by creating and distributing educational materials for health professionals and the public that enhance the delivery of safe and effective immunization services. IAC also facilitates communication about the safety, efficacy, and use of vaccines within the broad immunization community of patients, parents, healthcare organizations, and government health agencies.