How Do Vaccines Work? Understanding How Vaccines Train the Immune System 

Vaccines help the immune system recognize and respond to a disease-causing pathogen before a person encounters the actual infection. By exposing the immune system to a safe form or component of a pathogen, vaccines help the body build immune memory that can provide protection against future disease. 

Vaccines are one of the most important tools for preventing infectious diseases. But how do vaccines actually work, and how do scientists develop them? 

Researchers at the Texas Biomedical Research Institute (Texas Biomed) study infectious diseases and the immune responses they trigger, helping advance vaccines, therapeutics and other tools to protect human health. 

What is a vaccine? 

A vaccine is a biological preparation that trains the immune system to recognize a specific disease-causing organism or one of its components. 

Depending on the vaccine, it may contain an inactivated or weakened form of a pathogen, a specific piece of the pathogen, or genetic instructions that allow the body’s cells to temporarily produce a component that the immune system can recognize. 

The goal is the same: teach the immune system what to look for without requiring a person to experience the dangers of the actual disease. 

How do vaccines work? 

Vaccines work by activating the body’s natural immune response. 

When a person receives a vaccine, the immune system recognizes an antigen — a substance that triggers an immune response — as something foreign. Immune cells respond by producing antibodies and other defenses that are specific to that antigen. 

The immune system also develops memory cells. 

If the person later encounters the actual pathogen, these memory cells allow the immune system to respond more quickly and effectively than it could during a first encounter with the infection. 

A simple way to think about vaccination is practice for the immune system. The vaccine gives the immune system an opportunity to learn what a pathogen looks like before it encounters the real threat. 

What are antibodies and why are they important? 

Antibodies are proteins produced by the immune system that recognize specific targets on pathogens. 

Each antibody is designed to recognize a particular antigen. When the immune system encounters that antigen again, antibodies can help neutralize the pathogen or mark it for destruction by other components of the immune system. 

Vaccination can therefore create a pool of immune defenses that are ready to respond if the actual pathogen appears. 

But antibodies are only one part of the immune response. Vaccines can also stimulate cellular immune responses and the development of immune memory, which can contribute to longer-lasting protection. 

What are the different types of vaccines? 

Scientists have developed several approaches to creating vaccines. 

Inactivated vaccines 

These vaccines use a pathogen that has been killed or inactivated so it cannot cause the disease. 

Live-attenuated vaccines 

These vaccines use a weakened form of a pathogen. Because the pathogen is weakened, it can stimulate a strong immune response without causing disease in most people for whom the vaccine is recommended. 

Subunit or protein-based vaccines 

These vaccines use only a specific part of a pathogen — such as a protein — rather than the entire organism. 

Viral-vector vaccines 

These vaccines use a modified virus to deliver genetic instructions that help the body’s cells produce an antigen that stimulates an immune response. 

mRNA vaccines 

mRNA vaccines provide temporary genetic instructions that tell cells how to make a specific antigen. The immune system recognizes that antigen and develops an immune response. 

The mRNA itself does not become part of a person’s DNA. Instead, it provides temporary instructions that cells use to make the target protein before the mRNA is broken down. 

The development of mRNA vaccines for COVID-19 built on decades of research into the technology. 

Why do some vaccines require multiple doses? 

The immune system does not always develop its strongest or longest-lasting protection after a single exposure. 

Some vaccines therefore require multiple doses. Additional doses can strengthen the immune response, increase antibody levels and reinforce immune memory. 

Booster doses may also be recommended when protection decreases over time or when a pathogen changes enough that an updated vaccine is needed. The appropriate number and timing of doses are determined through research and clinical studies. 

Do vaccines prevent infection? 

Vaccines can provide different levels of protection depending on the disease and vaccine. 

Some vaccines are highly effective at preventing infection, while others are particularly important for reducing the risk of severe disease, hospitalization or death. 

No vaccine provides perfect protection to every person. Individual immune responses vary, and pathogens can also change over time. 

Even when vaccination does not completely prevent infection, reducing the severity of disease can provide an important public-health benefit. 

How are vaccines developed? 

Creating a vaccine is a lengthy scientific process. 

Researchers first need to understand the pathogen and identify an antigen that can produce a protective immune response. Scientists then develop and test potential vaccine candidates in laboratory studies and appropriate animal models. 

Before a vaccine can be tested in people, researchers need evidence about its safety and potential effectiveness. Human clinical trials then proceed through multiple stages, followed by regulatory review and continued safety monitoring after approval. 

This process can take years and involves scientists from many disciplines, as well as universities, research institutes, government agencies and pharmaceutical companies. 

What role does Texas Biomed play in vaccine research? 

Texas Biomed conducts research that can help move potential vaccines through the preclinical stage of development — the research that takes place before a vaccine candidate enters human clinical trials. 

The Institute combines infectious-disease expertise, high-containment laboratories and specialized animal research resources, including the Southwest National Primate Research Center. 

Texas Biomed’s vaccine-development approach includes studying pathogens, understanding immune responses, identifying whether an immune response is protective and testing vaccine candidates in appropriate research models. 

In preclinical vaccine research, scientists may first evaluate candidates in laboratory systems and smaller animal models. Promising candidates can then be evaluated in nonhuman primate models when scientifically appropriate. 

These studies can provide important information about whether a vaccine candidate generates an immune response and whether that response protects against infection or disease. 

Dr. Luis Martinez-Sobrido is developing a universal influenza vaccine with his team at Texas Biomed.

“The current vaccine works, but it’s not perfect since we need to be vaccinated every year,” said Dr. Martinez-Sobrido. “Our goal is to come up with a universal vaccine that will immunize people against all influenza strains, with long-lasting protection.”

Why are animal models used in vaccine research? 

Some infectious diseases affect humans and other primates in ways that cannot be fully replicated in cell cultures or computer models. 

Animal models can allow researchers to study complex interactions involving multiple organs and biological systems. They can also help scientists evaluate vaccine safety, immune responses and protection before a candidate moves into human clinical trials. 

Texas Biomed is home to the Southwest National Primate Research Center, one of seven federally supported National Primate Research Centers in the United States. Its combination of infectious-disease research, high-containment laboratories and specialized animal research resources allows scientists to conduct complex preclinical studies under controlled conditions. 

How does a vaccine protect against an infectious disease? 

The process can be summarized in five steps: 

1. Vaccination introduces an antigen or instructions for producing one. 

The vaccine exposes the immune system to a safe representation of the pathogen. 

2. The immune system recognizes the antigen. 

Immune cells identify it as foreign and begin mounting a response. 

3. The body produces antibodies and activates other immune defenses. 

These defenses target the specific antigen. 

4. The immune system creates memory. 

Memory B cells, T cells and other components of immune memory can remain after the initial response. 

5. The immune system responds more quickly during future exposure. 

If the person encounters the actual pathogen, the immune system is better prepared to respond. 

This ability to remember previous encounters is one of the fundamental reasons vaccines work. 

Why are vaccines important for emerging infectious diseases? 

Vaccines are particularly important when a new infectious disease emerges. 

Scientists may need to rapidly understand a pathogen, identify potential vaccine targets, develop candidate vaccines and determine whether those candidates generate protective immune responses. 

Research institutions such as Texas Biomed play an important role in this early stage of the vaccine-development pipeline. 

Texas Biomed has conducted preclinical research supporting vaccine development for serious infectious diseases, including Ebola. The Institute’s specialized facilities allow researchers to study infectious pathogens and potential countermeasures under appropriate containment conditions. 

What does vaccine research teach us about the immune system? 

Vaccine research is not only about developing a product to prevent disease. It also helps scientists understand one of the body’s most complex systems: the immune system. 

Researchers study questions such as: 

• Which parts of a pathogen trigger the strongest immune response? 

• Which antibodies can actually prevent infection or disease? 

• How long does immune protection last? 

• Why do some people respond differently to the same vaccine? 

• How can vaccines be designed to protect against rapidly changing pathogens? 

• How can scientists develop vaccines for diseases for which no effective vaccine currently exists? 

Answering these questions can help scientists develop better vaccines and deepen our understanding of infectious disease. 

The future of vaccine research 

Vaccine science continues to evolve. 

New technologies, improved understanding of the immune system and advances in genomics and computational biology are giving researchers new ways to design and evaluate vaccine candidates. 

At the same time, emerging infectious diseases continue to create new challenges. Viruses can evolve, pathogens can cross from animals into humans, and diseases that were once considered geographically limited can spread rapidly through an interconnected world. 

That makes vaccine research an important part of global health preparedness. 

At Texas Biomed, scientists study pathogens and the immune responses they trigger with the goal of helping develop the next generation of vaccines and other tools to prevent and treat infectious diseases. 

Frequently Asked Questions About Vaccines 

How do vaccines work? 

Vaccines train the immune system to recognize a specific pathogen or part of a pathogen. This allows the body to develop antibodies and immune memory so it can respond more quickly if it encounters the actual pathogen in the future. 

Do vaccines give you the disease? 

Vaccines are designed to stimulate an immune response without causing the disease they are intended to prevent. Different vaccines use different approaches, including inactivated pathogens, weakened pathogens, specific pathogen components or genetic instructions for producing an antigen. 

What is an antigen? 

An antigen is a substance that the immune system recognizes and responds to. In vaccines, an antigen can be a component of a pathogen or, in some vaccine technologies, the instructions that allow the body to produce the antigen. 

What is an antibody? 

An antibody is a protein produced by the immune system that recognizes a specific antigen. Antibodies can help neutralize pathogens or mark them for destruction. 

What is immune memory? 

Immune memory is the ability of the immune system to remember a previous encounter with a specific antigen. Memory cells allow the body to respond more quickly when it encounters the same pathogen again. 

Why do some vaccines need booster shots? 

Protection from some vaccines can decrease over time. Booster doses can strengthen and extend immune protection when research shows that additional doses are beneficial. 

How long does it take for a vaccine to work? 

The immune system needs time to develop protection after vaccination. The timing varies by vaccine and individual, and some vaccines require multiple doses to achieve optimal protection. 

Does Texas Biomed develop vaccines? 

Texas Biomed conducts basic and preclinical research that supports vaccine development. Researchers study pathogens and immune responses and evaluate vaccine candidates in laboratory and appropriate animal models before potential human clinical testing. 

Why is vaccine research important? 

Vaccines can prevent infectious diseases and reduce the risk of severe illness. Continued vaccine research is also important for preparing for emerging infectious diseases and developing new approaches against pathogens for which effective vaccines do not yet exist.