How Vaccines Work

Do you ever wonder how vaccines work?

To understand how vaccines work, I will give you a brief lesson on the immune system.

Trust me, it is interesting. Let me give you an example of me. When I was eight, I had chicken pox. It was a miserable week. I started out with fever and headache, then suffered days of intense body itching from blister-like spots, and ultimately, because I “scratched off” some scabs, ended up with scars.

During this time, my immune system cells worked to battle off the chicken pox virus. Immune cells called memory cells also formed. These cells have the unique job of remembering (hence the name “memory cells”) what the chicken pox virus looks like. Then, if ever in my life I was to contact chicken pox again, my memory cells could multiply and fight off the virus WITHOUT MY HAVING TO GET SICK AGAIN WITH CHICKEN POX. So after I was well again, I was able to play with my neighbor even while he suffered with chicken pox.  I even returned to school where other children in my class had chicken pox, but I did not catch chicken pox again. Even now, as a pediatrician, I don’t fear for my own safety when I diagnose a child with chicken pox, because I know I am immune to the disease.

This is an amazing feat, when you think about it.

And now, how vaccines work.

A vaccine contains some material that really closely resembles the actual disease you will protect yourself against. Today’s chicken pox vaccine contains an altered form of chicken pox that is close to but not actually the real thing. However, it is so similar to the real thing that your body’s immune system believes it is, in fact, real chicken pox. Just as in the real disease, your body mounts an immune response, and makes  memory cells that will remember what the disease looks like.  So, if you are exposed to another person with chicken pox, your body will kill off the virus but YOU DON’T GET SICK WITH THE CHICKEN POX. What a beautiful system!

Before chicken pox vaccine, about 100 children per year in the US died from complications of chicken pox disease. Many thousands were hospitalized with secondary pneumonia, skin infections, and even brain damage (encephalitis) from chicken pox disease. Now a shot in the arm can prevent a disease by creating the same kind of immunity that you would have generated from having the disease, only now you have one second of pain from the injection instead of a week of misery and possible permanent disability or death. I call that a Great Deal!

How vaccines are safer than the diseases they prevent.

All vaccines operate by this principle: create a safe environment for your immune system to make memory cells against a potentially deadly disease. Then when you are exposed to someone who actually has the disease, you will not “catch” it. Your body will fight the germs, but you do not become sick. If everyone in the world were vaccinated, then the disease itself would eventually be completely eradicated. This happened with small pox, a disease that killed 50 percent of infected people. There is no longer small pox because nearly everyone on earth received the small pox vaccine. Now we do not need to give small pox vaccine because the disease no longer exists. This is a huge vaccine success story.

Friedrich Nietzsche said “What doesn’t kill us makes us stronger.” We pediatricians feel this is unacceptable risk for children. We would rather see your child vaccinated against a disease in order to become immune rather than risking the actual disease in order to become immune.

Hopefully this blog post answers your questions about how vaccines work. For more details or more in depth explanations, I refer you to the AAP (American Academy of Pediatrics),  the Children’s Hospital of Philadelphia’s Vaccine Education Center, and the book Vaccines: What You Should Know, by pediatricians Dr. Paul Offit and Dr. Louis Bell.

Julie Kardos, MD and Naline Lai, MD

© 2009 Two Peds In a Pod®

updated 1/18/2015

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  • Reply Jessica R August 25, 2010 at 2:51 pm

    Can you please read this and comment?
    I’m terrified to vaccinated due to sites like these. There seems to be many horrifying stories out there to what happens to kids after getting vaccines. If the chance of them getting these diseases is small, is it worth taking the risk of them suffering these near death or death experiences?

  • Reply Drs Lai and Kardos September 3, 2010 at 2:47 am

    Thank you so much for taking the time to comment. It looks like you are trying to sort through information to make a well informed decision about your child. You’re right, it can be confusing to sort out fact from fiction on the internet. Because we know others share your concerns, we have addressed yours in a separate post. Please see: Evaluating Vaccine Sites on the Internet

  • Reply Should I vaccinate my child? | Two Peds in a Pod® January 25, 2015 at 9:58 pm

    […] from our earlier 2011 post Visit these posts for more infomation about vaccines: How Vaccines Work, Evaluating Vaccine Sites on the Internet, Do Vaccines cause autism? and Closure: there is no link […]

  • Reply Evaluating Vaccine Sites on the Internet | Two Peds in a Pod® September 20, 2015 at 4:24 pm

    […] In addition, we encourage you to read our own vaccine posts: How Vaccines Work and Do Vaccines Cause Autism? Please visit the websites we provide in these articles for more […]

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