How Vaccines Prevent Disease

Our bodies have several lines of defense against

infections and disease. Our immune system is

made up of cells, tissues, and organs working

together to fight off infections.

Your immune system fights pathogens that have already invaded your body. Vaccines are able to protect you against diseases before you actually get them. How do vaccines protect you against disease? They use the body’s defense system to produce disease-fighting antibodies. When you are later exposed to the disease, your body already has defenses in place to fight the disease, and you don’t get sick.

Read on to find out more about vaccines and how they protect you against disease.

Learning Objectives

By the end of this lesson, students should be able to:

Describe how a vaccine produces immunity to a disease.
Distinguish between active immunity and passive immunity.
Explain the function of the body’s immune system.

Vocabulary

active immunity—resistance to disease acquired by either exposure to a pathogen or by receiving a vaccine against a pathogen.

antibodies—a substance made by the body in response to an antigen.

antigen—any type of substance that the immune system recognizes as foreign to the body and that can trigger an immune response.

B cells—a white blood cell that produces antibodies that bind to an antigen.

disease—a condition in which the body cannot function normally due to infection by a pathogen or an illness of a body organ.

herd immunity—resistance to a disease by a community; having a large number of immune persons in a community lowers the chances that an infected person will come into contact with a susceptible person among the population.

immune system—the body system that is involved in producing defenses against disease.

immunity—resistance to disease.

infection— a condition in which a pathogen invades the body and begins to multiply.

lymphocyte—a white blood cell.

passive immunity—immunity that is produced from the body’s response to antibodies that have not been produced by the body’s own immune system.

pathogen—an organism that causes disease.

vaccine—a solution made from a killed or weakened virus; produces immunity to a disease.

Your Immune Response

Your body has several types of defense against disease. Your skin provides protection against many pathogens (disease-causing organisms) entering your body. As long as the skin is not broken, helpful bacteria on the skin can destroy many harmful bacteria you may encounter.

But, sometimes bacteria and other pathogens can enter the body. Your immune system contains cells that can fight off bacteria and viruses that enter the body through your nose, eyes, mouth, and cuts in the skin. Cells called macrophages fight off the pathogens by engulfing and destroying them. Other cells called lymphocytes produce antibodies that fight the pathogens.

How do cells and antibodies fight disease? Lymphocytes are white blood cells that circulate through the blood. When they encounter a foreign particle (called an antigen) in the blood, they produce antibodies. Antibodies are special proteins that can attach to the antigen and make it harmless. As the antigens of viruses are deactivated and made harmless, you fight off the disease and you get better.

Antibodies can produce lasting immunity to a disease. The antibodies produced by lymphocytes stay in the blood. If you encounter the same pathogen again, the antibodies you already have fight off the disease and you don’t get sick again.

For example, if you have had chicken pox, you probably have immunity (the ability to resist disease) to chicken pox. You formed antibodies to chicken pox when you were infected with it and most likely cannot get it again. The antibodies you formed the first time fight off the disease when you come into contact with it again. Remember: Specific antibodies are made by the body for specific antigens. If you have antibodies against chicken pox, they protect you against chicken pox, but not mumps. This is called active immunity. You have the ability to resist the disease because you actively made the antibodies that protect you.

Another type of immunity is passive immunity. Passive immunity occurs when antibodies which have been produced by another animal are given to you so you will not get sick. Passive immunity does not last as long as active immunity. You have to get booster shots from time-to-time so that you maintain immunity to the disease

But, there is a way you can have immunity to a disease

without having to ever get it. You can get immunized

against a disease by getting a vaccine. A vaccine causes

the body to make antibodies against a specific disease. Whenever

disease organisms enter the body, the antibodies are already present to destroy them. You do not have to get sick to be protected.

Passive immunity example: Tetanus is a disease caused by a bacterium. Tetanus produces a toxin that paralyzes muscles. Death occurs by suffocation when the toxin paralyzes muscles that control breathing.

Tetanus vaccines are made by other animals and then given to humans to provide immunity to the disease. Booster shots of the tetanus vaccine are needed throughout life, especially after puncture wounds.

Vaccines have saved millions of lives worldwide. Diseases that once ravaged populations are now preventable.

Fast Fact: Why do you get a flu shot every year if active immunity is long-lasting?

Flu viral strains change from year to year. Scientists research which strains are most likely to be circulating in the population each year and produce a vaccine to protect against the most prevalent strains. The flu shot you get is a different one each year.

The Importance of Vaccines

The first vaccine was invented by a British doctor, Edward Jenner, against smallpox in the late 1790s. In 1980, the World Health Organization (WHO) promoted a worldwide vaccination program to eliminate smallpox disease.

In the 1950s, Drs. Jonas Salk and Albert Sabin

developed vaccines against polio. Polio can be a

severe, crippling and sometimes deadly disease

which affect the nervous system. It often paralyzes

its victims. Because you have been vaccinated

against polio, you have almost no chance of getting

this disease.

There are quite a few vaccines that can protect

you against disease, including measles, mumps, tetanus, diphtheria, hepatitis, pneumonia, influenza and chicken pox.

Image: A man showing the effects of polio. Content: CDC/NIP/Barbara Rice http://phil.cdc.gov/phil/details.asp

Some of these diseases have begun to reappear, however. In 2019, the Center for Disease Control and Prevention (CDC) reported more than 1,250 cases of measles even though this disease is preventable by vaccination. This was the greatest number of cases reported in the U.S. since 1992. The majority of cases are among people who were not vaccinated against the disease.

Many people think that measles is a mild childhood disease, but measles can cause severe complications. Vaccination is the only way to ensure protection against this disease.

Check Your Understanding

1) Explain how your blood cells work to fight off disease.

2) How does a vaccine produce immunity to a disease?

3) Explain passive immunity.

4) Why do you need booster shots sometimes?

Young girl smiling as she gets a vaccine from a doctor.a vaccine

Two bottles of vaccine and one syringe sitting on a table.