To understand how vaccines work, it helps to first look at how the immune system works.
The immune system is a network of organs, cells and tissues that work together to protect the body against disease.
When a disease-causing germ, like a virus or bacteria, enters the body, the immune system responds by making proteins called antibodies. These antibodies work with the rest of the immune system to destroy the germ.
The first time the body gets exposed to a germ, it takes time for the immune system to respond and produce antibodies. In the meantime, a person could become sick. But after the first encounter, the immune system usually remembers the germ and how to fight it. Then, if the body is exposed to the same germ again, the immune system can quickly respond and destroy the germ before it makes a person sick.
Vaccines teach the immune system how to recognize and fight off specific disease-causing germs. They help protect you against disease without the risk of getting sick first.
Vaccines contain killed, weakened or synthetically manufactured versions of the disease-causing germ or parts of the germ called antigens. Some newer vaccines (e.g., COVID-19 mRNA vaccines) contain instructions for producing antigens rather than the antigen itself.
When a person gets a vaccine, the immune system responds to the antigen as if it were exposed to the actual germ (it makes antibodies and remembers how to defeat it). Then, if the body gets exposed to the actual germ, the immune system can recognize it right away and quickly fight it off to prevent disease.
While most vaccines are highly effective in preventing disease, no vaccine is 100% effective. Not all people get full protection after immunization. But those who get a disease after being immunized are less likely to become seriously ill.
It's much safer to get a vaccine than to get the disease it prevents.
When you get immunized, you’re not just protecting yourself — you’re also helping to protect your entire community. This is because the more people in a community who are immune to a disease (either though immunization or prior infection), the harder it is for a disease-causing germ to spread from person to person — and the entire community is less likely to get the disease. This type of protection is called community immunity (or herd immunity).
Community immunity helps protect everyone, but it is especially important for protecting people who cannot get immunized, such as very young babies and people with certain medical conditions, like a child receiving treatment for cancer. Community immunity is also important for people who may not receive full protection from immunization, such as those with weakened immune systems.
No vaccine is 100% effective, and community immunity does not provide full protection to those who cannot be protected from vaccines. But these people will have less of a chance of getting sick, thanks to those around them being immunized.
Community immunity is another important reason to ensure you and your family get all the recommended vaccines.
Learn about the science behind vaccines and how they work.
A look at how vaccines and group immunity can protect you, your family and your community.
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