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How Do Vaccines Work?

By Emily Sheng

Image from Freepik

Imagine that you are at your annual doctor’s appointment. The nurse has kindly taken your height and weight, and you are led to the private room in the back. Everything goes well until the mention of vaccines. The doctor tells your parents that the government recommends a certain vaccine for kids your age. Goosebumps appear out of nowhere as the thought of a long and pointy needle pops up in your mind.

Why do these scary vaccines exist? What do they do?

Vaccines allow your body’s immune system to protect against infectious diseases. The immune system prevents you from getting sick from all the germs around you.

Your body’s immune system has many methods to fight against germs. It has two major systems, one being the innate immunity and the other being the adaptive immunity.

Innate immunity provides general defense against germs. For example, your body produces a thick slimy substance called mucus in your respiratory pathway that can trap germs from entering your body through your nose or mouth.

Adaptive immunity provides a specific defense against germs through humoral and cell-mediated immunity. B cells and T cells, two kinds of white blood cells, are the superheroes of this defense system. B cells provide humoral immunity by producing antibodies that can prevent germs from infecting your body. These antibodies can block the germs from infecting your cells and can help make your innate immunity system stronger. T cells provide cell-mediated immunity by directly attacking and killing the infected cells.

If you get exposed to a germ, your body will simultaneously use both immune systems to fight the infection. It is during the infection period that you begin to have a fever, headaches, and other uncomfortable symptoms. After you have recovered, your body is able to remember what germ caused the illness through memory B and T cells. This allows your body to be better prepared to fight the germ the next time.

Vaccines are able to mimic a natural infection without most of the annoying bodily aches and pains. They provide artificially acquired active immunity since they are purposely given to you by the doctor, and your body responds by producing its own immune response. Thus, vaccines are also able to leave behind a whole army of B and T cells to beat the germs before you even get infected!

Image from BBC

There are many different types of vaccines based on what kind of virus or bacteria it is fighting against, how the germs cause an infection, and which method is the safest.

Live attenuated vaccines are vaccines that contain a modified, weakened form of the virus or bacteria. This allows the germ to infect the body but not cause serious symptoms. They generally provide lifetime protection because of how close it imitates a natural infection. Some examples are the measles, mumps, and rubella (MMR) vaccine or the chickenpox vaccine.

Another major type of vaccine are inactivated vaccines. These vaccines contain killed or inactivated germs. The bacteria and virus are grown in culture, but then are killed with heat and chemicals and later purified. These are not as effective as live attenuated vaccines are and require multiple doses. However, since they do not contain any live germs, they are safer than live attenuated vaccines. An example is the polio vaccine.

A special kind of vaccine that doesn’t contain any portion of the germ itself, but a chemical produced by the germ is a toxoid vaccine. These vaccines contain a harmful chemical, called a toxin, made by the germ. This allows your body to protect against the dangerous chemical produced by the germ. The toxin is inactivated by treating it with chemicals or heat. An example is the diphtheria and tetanus vaccine.

Newer types of vaccines are subunit and conjugate vaccines. Subunit vaccines use only a part of the germ like a viral protein. Similarly, conjugate vaccines use only parts of the outside of the bacteria. An example is the pneumococcal vaccine.

Types of Vaccines

So, the next time you are at the doctor’s and are waiting for the nurse to give you the shot, remember that the simple vaccine you are getting can protect you from getting sick with that disease for a very long time.



Editor: Judy Zhang

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