How Do Vaccines Work in the Body?

As parents, your child's well-being is always at the forefront of your mind. We understand that navigating health information can be complex, and questions often arise, especially when it comes to something as vital as vaccines. Here at Lurie Children's, we want to help you understand exactly how vaccines work to keep your little ones safe and healthy. Dr. Taylor Heald-Sargent, Attending Physician in Lurie Children's Division of Pediatric Infectious Diseases, explains everything parents need to know about how vaccines work and why they are so important for children.

Understanding the Immune System

The body has many ways of defending itself against pathogens — the germs that cause diseases. When a new germ enters the body, the immune system identifies unique "flags" called antigens and then creates specialized proteins called antibodies to fight them off.  
 
Once antibodies are made, the immune system remembers how to fight that specific germ, providing long-term protection. However, the first time a child encounters certain bacteria or viruses can sometimes lead to severe illness, hospitalization, or even worse outcomes, especially for young children whose immune systems are still developing. 

What do vaccines do?

Vaccines work by training your child’s immune system to recognize and fight off specific diseases. Once administered, a vaccine introduces a safe, weakened, or inactive version of a virus or bacteria. This prompts the body to produce antibodies, just as it would during a real infection. 
 
These antibodies provide long-term protection, so if your child is ever exposed to the real disease, their immune system can quickly recognize and fight it off before it causes severe illness. Some vaccines require more than one dose to build a lasting memory of the pathogen and ensure long-lived antibodies. 
 
Vaccines do not cause any illnesses and only contain a small fraction of the antigens that your child comes in contact with every day. Most children can and should receive all recommended vaccines. However, there are specific medical reasons why a child might not be able to receive a certain vaccine or might need to delay it. If you have any concerns about your child's health and vaccinations, speak with your pediatrician. 

Why are vaccines so important for children?

Young children and infants are especially vulnerable to serious complications from vaccine-preventable diseases because their immune systems are still maturing. Vaccines provide a crucial head start, protecting them during their most susceptible years. 
  
Furthermore, widespread vaccination creates herd immunity. When enough people are immunized, it makes it much harder for a disease to spread, protecting babies too young to be vaccinated, individuals with weakened immune systems and others who cannot receive certain vaccines. 

What do vaccines prevent?

Vaccines primarily prevent infectious diseases caused by specific viruses or bacteria. Here's a list of some of the common and serious diseases that vaccines prevent: 

• Measles
• Mumps
• Rubella (German Measles)
• Polio (Poliomyelitis)
• Diphtheria
• Tetanus (Lockjaw)
• Pertussis (Whooping Cough)
• Hepatitis A and Hepatitis B
• Haemophilus influenzae type b (Hib)
• Pneumococcal disease
• Rotavirus
• Chickenpox (Varicella)
• Influenza (Flu)
• Meningococcal disease
• Human Papillomavirus (HPV), which can prevent certain types of cancer
• COVID-19
• Respiratory Syncytial Virus (RSV)

Vaccines are among the safest and most effective medical interventions available. They undergo extensive research and rigorous testing for many years before being approved for use. The potential side effects from vaccines (usually mild and temporary) are minimal compared to the serious and life-threatening risks of the diseases they prevent. 
 
Due to widespread vaccination efforts, some diseases have been eliminated worldwide. Continuing to vaccinate ensures these diseases do not make a comeback. Learn more about childhood vaccinations here.  

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