What are Vaccines and Why are they Important?

Last week, a series of news stories left me both frustrated and concerned. RFK Jr., our current U.S. Secretary of Health and Human Services, announced plans to cut funding for mRNA vaccine projects. Around the same time, misinformation about vaccines reportedly motivated a young man to walk into a CDC campus with a gun, killing an officer. His rumored intent being rooted in hatred for the COVID-19 vaccine.

Moments like these remind me just how dangerous misinformation can be. Despite decades of solid scientific evidence, fear and doubt still cloud public perception of vaccines. Instead of sitting in frustration, I want to use this space to break down the facts – what vaccines are, how they work, the different types, and why they are a cornerstone of public health.

I’m not claiming to be an immunology expert, but my background in biomedical sciences gave me a solid foundation in vaccine science. Much of what I know comes from my time at SIUE – so, big shoutout to Professor Christine Simmons for sparking my passion for understanding this subject. My hope is that by sharing what I’ve learned, you’ll feel more equipped to make informed decisions about your own health and speak confidently about vaccines with others.

So, what are vaccines? At their core, vaccines are biological preparations that train the immune system to recognize and fight specific pathogens – without causing the actual disease. Think of them as a rehearsal for your immune system, so it’s ready for the real performance if the pathogen ever shows up.

To understand how this works, it helps to have a basic grasp of the immune system itself. The immune system is our body’s built-in defense network. Its job is to protect us from invaders that could cause harm. These invaders are detected by their antigens – substances that the immune system can identify as foreign and potentially dangerous. When an antigen is detected, the body mounts an immune response – the mechanism by which the immune system reacts to an antigen that may look and feel like pain, swelling, redness, inflammation, or fever.

In this battle, the immune system sends out its ‘warriors’: T cells, B cells, natural killer cells, basophils, and more. Once these defenders figure out how to neutralize an antigen, they store that knowledge in the body’s immunological memory. The next time the same antigen appears, the immune system recognizes it instantly and defeats it more quickly and efficiently. This ability to remember is exactly what vaccines tap into. They give your immune system the blueprint for fighting a pathogen before you ever encounter the real threat.

Vaccines work by safely mimicking an infection, prompting the immune system to recognize and respond to the antigen, without causing the actual disease.

There are several different types of vaccines, each designed to protect against disease in a unique way: 

Whole pathogen vaccines

Whole pathogen vaccines use the entire pathogen to trigger an immune response. They come in two main types:

Live, attenuated vaccines – These contain live pathogens that have been significantly weakened so they can no longer cause disease in healthy individuals. An example is the Measles, Mumps, and Rubella (MMR) vaccine. While highly effective, these vaccines may not be suitable for people with weakened immune systems, but are safe for the general population.

Inactivated (killed) vaccines – These contain pathogens that have been killed using heat or chemicals, preventing them from replicating or causing disease. An example is the polio vaccine. Because they cannot replicate, these vaccines often produce a weaker immune response and may require multiple doses or booster shots for full effectiveness.

Subunit Vaccines

Subunit vaccines use specific parts of a pathogen to trigger an immune response without causing infection. These components may include proteins, polysaccharides, inactivated toxins, or conjugates from the original pathogen. A conjugate is a polysaccharide linked to a protein to improve immunogenicity – the ability to elicit an immune response. Because these vaccines do not contain the entire organism, they cannot cause disease. Subunit vaccines are often developed when using a whole pathogen could pose safety concerns, or when only certain antigens are needed to provide sufficient protection. An example of this is the Hepatitis B vaccine.

Particle-Based Vaccines

Particle-Based vaccines use outer membrane vesicles or virus-like particles to imitate the structure of harmful microbes, but they contain no infectious material. This allows the immune system to “train” on something that looks like the real pathogen without the risk of causing illness. By learning to recognize and attack these harmless particles, the body is better prepared to respond quickly if exposed to the actual pathogen. These vaccines cannot replicate or cause disease, yet they are highly effective at stimulating a strong immune response. A well-known example is the HPV vaccine, which uses virus-like particles.

Vectored Vaccines

Vectored vaccines use a harmless microorganism as a carrier to deliver genetic material that encodes the target antigen. Once administered, the vector enters host cells and produces the antigen, prompting the immune system to respond. This method can generate strong cellular and humoral (antibody-mediated) immune responses. Vectored vaccines are especially valuable when delivering the antigen directly is difficult using other vaccination methods. An example of this approach is the Ebola vaccine.

Nucleic Acid-Based Vaccines

Nucleic acid-based vaccines use DNA or mRNA to instruct the body’s own cells to produce the antigen. Once the antigen is synthesized, the immune system recognizes it as foreign and launches a defense. While both DNA and mRNA vaccines work toward the same goal, they operate slightly differently in the body.

DNA vaccines – These vaccines deliver plasmid DNA into host cells. A plasmid is a circular, double-stranded DNA molecule, distinct from the organism’s chromosomal DNA. Once inside the cell, the DNA enters the nucleus, where it is transcribed into mRNA using the body’s own processes. The mRNA then exits the nucleus and is translated into the antigenic protein by the cell’s ribosomes. The immune system detects this protein and responds accordingly.

mRNA vaccines – These vaccines deliver mRNA directly to the cytoplasm, bypassing the nucleus entirely (and therefore never interacting with the cell’s genetic material). Once inside, ribosomes immediately translate the mRNA into the antigenic protein. This rapid antigen production triggers both humoral (antibody-driven) and cellular (defensive “warrior” cell) immune responses. The Pfizer and Moderna COVID-19 vaccines are well-known examples of this technology.

Overall, nucleic acid vaccines represent a major breakthrough in vaccine technology, enabling rapid development and robust immune activation. Ongoing research is expected to expand their applications to a wider range of infectious diseases and even cancer immunotherapy.

Alright, we know a bit about the kinds of vaccines we use. Now, let's talk about why vaccination is important. Vaccines protect us against serious illness or death. They also increase herd immunity, which means they reduce the spread of diseases across communities because more people are protected. Herd immunity is especially vital for immunocompromised individuals who may not be able to receive a vaccine.

Vaccination can even help us eradicate diseases. A prime example is smallpox. Smallpox used to be one of the deadliest diseases, and most people who contracted it did not survive. But thanks to vaccination, it has been completely eradicated. Finally, getting vaccinated prevents long, costly hospitalizations and long-term health problems caused by illness.

So why are we so scared of getting vaccinated? Well, just as a virus can spread rapidly throughout our bodies, misinformation spreads quickly online. This misinformation creates distrust in vaccines, often based on untested claims from people who aren’t experts in this field of science. We also distrust our institutions, but it’s important to remember that these institutions benefit more when we stay alive than when we suffer adverse effects from vaccines.

Another reason for fear is that we sometimes mistake side effects for illness. When we get vaccinated, our bodies mount an immune response. You might experience redness, swelling, inflammation, pain, or temporary reductions in function while your body learns how to defeat the antigen. Feeling a bit under the weather after a vaccination is completely normal. Science shows that side effects are usually mild and temporary, serious adverse events are extremely rare, and the benefits of vaccination far outweigh the risks.

That said, transparency is crucial. Science should always be open about limitations and risks—but transparency is not the same as fueling unfounded fear.

Vaccines are among the safest and most effective public health tools ever created. They protect us from succumbing to devastating diseases. When healthy people go to the doctor and get vaccinated, we protect ourselves—and our communities—from serious illness. Vaccines aren’t about control; they give us freedom from preventable disease.

If you still have questions or do not believe everything I have said in this post feel free do to your own research on disease and vaccines or reach out to me and ask questions. I am not an expert, just a person with a bachelors degree in biomedical sciences.