How Do Vaccines Prevent Us from Getting Sick?

December 2, 2019

The bottom line: Vaccines work to prevent people from catching infectious diseases. Here’s how: They introduce a dead or weakened version of the virus or bacteria to train our natural defenses to kick in. If our body faces a real threat from the live germ later, the immune system is armed to block it from harming us.

Most people accept the fact that vaccines protect them from diseases. But many still wonder: how do they work?

Most everyone’s immune system works effectively to help them fight off illnesses. A vaccine is like a trainer for that system, reports December’s Texas Medical Association (TMA) Texas Medicine magazine. When a physician or other health care worker gives someone a shot, that patient’s body thinks the vaccine is an invading disease. So the body creates a defense against it. The shot triggers a person’s natural defenses to build up against what it perceives to be an infectious attacker. If the real disease ever does attack, the body is ready for it. Those defenses kick in, and thwart the attack.

The Centers for Disease Control and Prevention describes it this way: “Vaccines contain a small number of weakened or dead antigens, the parts of germs that cause [someone’s] immune system to go to work. After [the person] receives a vaccine, their immune system – or antibodies in the system – will remember that antigen and attack it if it ever enters the body again.”

Because scientists make vaccines from a weakened or dead version of a germ, they almost always are too weak to make a person sick. The person’s immune system recognizes the antigen as a threat and responds, building up immunity to the disease.

“Vaccines have been a huge advance we’ve seen in the last century that have made an enormous impact on the health not only of Texans and the United States, but of the entire world,” said Jennifer Shuford, MD, in a TMA video. Dr. Shuford is the infectious disease medical officer for the Texas Department of State Health Services, and consultant to TMA’s Committee on Infectious Diseases. 

Historians say the concept of vaccinating originated in Asia and Africa before the 18th century, as a practice called variolation. The process involved exposing a healthy person to matter from an infected person’s smallpox blisters, either through an opening in the skin or by inhaling up the nose. Variolation was successful in protecting many people from smallpox, but others became severely ill and died. 

Edward Jenner, who studied science and medicine in England, heard that dairy maids who contracted cowpox virus from infected cattle would get a mild illness and would then be immune to the deadly, highly contagious smallpox virus. He applied a technique similar to variolation in the late 1700s to an 8-year-old boy, James Phipps, by inoculating the boy with matter from a cowpox blister. He later introduced smallpox to the boy, who did not get sick. This practice, which was safer than variolation, became more widespread thereafter.  

The Latin word for cow is vacca, so Mr. Jenner chose to call this new procedure vaccination. Physicians today understand how vaccinating works, and want patients to understand it, too.

“Talk to your physician about this issue,” Dr. Shuford recommends. “They have a lot of experience looking at the scientific research as well as experience dealing with vaccine-preventable diseases. They want to hear your concerns and they want to be sure to address every concern you have as a parent and as a patient.”

TMA continues to highlight contagious diseases that childhood and adult vaccinations can prevent, including measles, chickenpox and shingles, pertussis (whooping cough), and many others. TMA also addressed the autism myth. TMA has worked to raise immunization awareness and fight back against false claims that hamper immunizations. 

TMA is the largest state medical society in the nation, representing nearly 53,000 physician and medical student members. It is located in Austin and has 110 component county medical societies around the state. TMA’s key objective since 1853 is to improve the health of all Texans. 

Be Wise – Immunize℠ is a joint initiative led by TMA physicians and medical students, and the TMA Alliance. It is funded in 2019 by the TMA Foundation thanks to H-E-B, TMF Health Quality Institute, Pfizer Inc., and gifts from physicians and their families. 

Be Wise – Immunize is a service mark of the Texas Medical Association. 


TMA Contacts:  Brent Annear (512) 370-1381; cell: (512) 656-7320; 

 Marcus Cooper (512) 370-1382; cell: (512) 650-5336

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Last Updated On

January 31, 2020

Originally Published On

December 02, 2019

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