What Are Vaccines?

Contributor: Hannah Brooks. Lesson ID: 12697

Nobody likes to be sick, and the medical world strives to prevent and eliminate disease. So, why would you purposely inject someone with pathogens? This is part of vaccination, a way to fight illness!


Life Science

learning style
personality style
Grade Level
Middle School (6-8), High School (9-12)
Lesson Type
Dig Deeper

Lesson Plan - Get It!

  • Why do babies and small children get so many shots?

Babies and children are exposed to — and vulnerable to — many different diseases and pathogens as they grow up.

Pathogens are viruses and bacteria that cause disease. Immunizations and vaccines can help prevent the transmission of these infections. These medications work by helping your body recognize and remember the antigen, or toxin, that the immune system works to destroy, that can cause diseases like diphtheria, measles, mumps, and rubella. Immunization allows your body to respond to the pathogen faster than a typical immune response. Some vaccines provide long term immunization, or protection, from a disease, while others must be followed-up with additional doses.

Before continuing on, if you missed or need to review the previous lesson in this Immune System series, find it under Related Lessons in the right-hand sidebar.

There are three main types of vaccines used today: live, inactive, and subunit vaccines.

  • Live vaccines use a weakened sample of the pathogen or microbe so that it does not cause the disease, but provides enough exposure so the immune system is able to remember it. Live vaccines usually provide long-term immunization after one or two doses. Individuals who have weak immune systems should not receive live vaccines because there is a greater chance of the live microbe replicating and causing an infection. These vaccines must also be refrigerated, which makes shipping and distribution to remote areas difficult.

Examples of common live vaccines include measles, chickenpox, and mumps. Diseases caused by viruses are easier to prevent with live vaccines because viruses remain stable over time. Bacteria often mutate and change, so using live vaccines would be inefficient.

  • Inactive vaccines use dead microbes to produce the medication, so they do not require refrigeration and are easier to distribute. Since these produce a lower immune response than live samples, several doses are required to reach immunization. Have you ever gotten a booster shot? That is an inactive vaccine! Tetanus is a good example of an inactive vaccine because it prevents an infection due to exposure to the tetanus bacteria.

  • Finally, subunit vaccines use the antigens from a microbe or pathogen to cause an immune response. This prevents accidental infection from introducing the whole pathogen. The immune system is able to identify and remember the antigen associated with the microbe without coming into contact with the invader. An example of a subunit vaccine is Hepatitis B, which protects against viral infection.

These three types of vaccines help prevent many infectious diseases by exposing the human immune system to small samples of viruses, bacteria, and pathogens. In allowing the human body to identify small samples, it allows the body to effectively fight off future exposure that could lead to disease or death.

Scientists and doctors use different types of vaccines to protect against different diseases, based on where the disease originates from and logistics such as storage. While live samples offer higher immunity, they are also harder to store and ship. Inactive vaccines are easier to distribute but often require multiple doses to reach immunity. Subunit vaccines prevent accidental infection but require a great deal of lab work to prepare.

  • What have you learned about the types of vaccines used in modern medicine?

Middle school students should discuss the three types of vaccines with a parent or teacher. High school students should create a graphic organizer that explains the three types of vaccines in a notebook.

  • Is there a vaccine you wish we had access to? Why?

In the Got It? section, you will learn more about the controversy surrounding mandatory vaccinations in the United States.

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