How Do Vaccines Work?

How Do Vaccines Work?

There has been an increased interest in vaccines since the Covid-19 pandemic started. Certainly, there have been small interest groups that have invested interest in vaccines, but it seems as though now the whole world has become interested in how vaccines work. Parents, in particular, want to know how vaccines work as the development of new vaccines for children is underway in the global effort to tackle the pandemic. Consider this article your vaccine introductory course. We will cover what a vaccine is, how they work, what vaccines are currently available to small children, and how to prepare your child for their shot appointment. 

What is a vaccine?

A vaccine is a shot administered by a medical professional, such as a pharmacist, nurse, or doctor. It is designed to protect an individual from whatever illness the vaccine was created for. Every vaccine is created to protect an individual’s immune system from a specific illness. For example, the flu vaccine works to protect an individual’s immune system from the flu. In the US, there are dozens of available vaccines meant to keep people healthy. The more individuals in a given population who are protected from a certain illness, the healthier the community is as a whole. Historically, vaccines have been critical in eliminating, or strongly reducing, the threat of illnesses such as polio, smallpox, and measles. 

person holding injection
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How does it work? 

While each vaccine varies slightly in how they work, the general principle is the same. Vaccines, “familiarize your immune system-which makes antibodies to defend your body against harmful invaders–with a certain pathogen so that it will know what to do if you become infected with that pathogen in the future” (Cleveland Clinic 2021). When our immune system has been vaccinated, it learns how to fight off a disease. Vaccines are able to do this by triggering the immune system, each vaccine contains one of the following (Cleveland Clinic 2021):

  • A weakened form of a pathogen
  • An inactive form of a pathogen
  • Certain parts of the pathogen, such as its proteins
  • A weakened toxin made by the pathogen

By preemptively exposing the immune system to a weakened form of the diseases, the immune system learns how to create the antibodies needed to fight off the disease. Then when exposed to the disease in its full form, the immune system can more readily protect itself. 

What are vaccines made of? 

As mentioned before, vaccines contained some form of the weakened disease. Additionally, there are other ingredients in a vaccine that help it work effectively. These include (OIDP 2021): 

  • Cell culture (growth) material, like eggs, to help grow the vaccine antigens.
  • Inactivating (germ-killing) ingredients, like formaldehyde, to weaken or kill viruses, bacteria, or toxins in the vaccine.
  • Antibiotics, like neomycin, to help keep outside germs and bacteria from growing in the vaccine.

There are sometimes other ingredients that are used to keep the vaccines safe and long-lasting as far as shelf life is concerned. Examples of those ingredients include (OIDP 2021):

  • Preservatives, like thimerosal, protect the vaccine from outside bacteria or fungus. Today, preservatives are usually only used in vials (containers) of vaccines that have more than 1 dose. That’s because every time an individual dose is taken from the vial, it’s possible for harmful germs to get inside. Most vaccines are also available in single-dose vials and do not have preservatives in them.
  • Stabilizers, like sugar or gelatin, help the active ingredients in vaccines continue to work while the vaccine is made, stored, and moved. Stabilizers keep the active ingredients in vaccines from changing because of something like a shift in temperature where the vaccine is being stored.

Each vaccine will vary in terms of what it is specifically made of, but generally they all contain some combination of the ingredients listed above. 

What is revaccination?

Revaccinations are common; they are simply an additional dosage of the vaccine. How often you will need to be revaccinated depends entirely on what you are being vaccinated for. Some vaccines, such as the MMR vaccine, require two doses (spaced a few years apart) to take full effect, but rarely will you need any additional MMR vaccination. Other vaccines, like the tetanus vaccine, wear off over time and will require a booster shot after ten years. Then there are other examples, like the flu vaccine, where annual vaccinations are recommended because the immune response shifts slightly from year to year (Cleveland Clinic 2021). Revaccination is a broader term for “second dose” or “booster shot” which are more commonly used terms.

How are children vaccinated and what vaccinations are given to children? 

Children are vaccinated very similarly to adults, the exception being that infants and very young children receive their vaccine in the thigh whereas older children and adults receive a vaccine in the arm. 

Photo credit: CDC

You can find more information about the US recommended vaccine schedule here

Schools and daycares often track which students have had which vaccines, it is also common for vaccination to be a requirement to attend. You can have your doctor send your child’s vaccination records to the school nurse or daycare provider if this is the case. Being ontop of your child’s vaccine schedule is important. 

How to prepare a child for vaccination? 

Each child is going to respond differently to their shots appointment. I find that for children who are 3 years and older, it’s important to be honest to be upfront about what to expect at the appointment. Children who are younger may struggle to rationalize what is being expected; the toddler years are hard. Here are some tips to help prepare your child for the appointment:

  • Give them time to process. Letting your child know 10 minutes before the appointment may cause panic, making it difficult to settle them down and cooperate during their visit. I give my daughter a day’s notice so she has a night to sleep on it. Some kids like to “count down” the days to the appointment and find that 3 days
  • Answer any questions they may have about their shot. They will want to know how much it hurts and how long it will take. Be honest, it’s going to hurt. Then assure them it doesn’t hurt too bad and it’s over fast. My daughter actually watched a little video of a nurse giving a shot so she could see what it looks like. Knowing what to expect can help calm their fears. It’s important to validate their feelings, but not their fears. Yes, they can be scared and that’s normal; however, there is nothing to be afraid of.
  • Make sure they feel secure. Either by holding them during the appointment or bringing a blanket or stuffed animal from home that helps them to feel secure. Each child will vary about what they will want during the shot. Ask your child if they want to sit in your lap, hold your hand, or bring a security item from home. Maybe even all of the above.
  • Reward them for their cooperation. I tend to overhype the reward my daughter gets after she gets her shot but it can help give them something to look forward to after the appointment. For us, we go out and get a cupcake afterwords. Do what works for your family and know that it might become a shot “tradition” so pick a reward you can replicate. It’s also to reward them even if they don’t necessarily “cooperate”, so long as they got their shot, we go for the reward. Crying and panicking aren’t bad behaviors, just very big feelings for little people.
  • Talk about it afterward. I like to ask my daughter about how she felt the appointment went afterward, usually as she is enjoying her reward. This can help create a learned sense of “I can do this” when it comes to shots. That way going foward, they will remember they have done this before and they were able to move on. 

Final thoughts

Given everything we know about vaccines, it is safe to say that vaccines are critical to protecting and preserving the health of an individual as well as the community as a whole. If you are concerned about the safety of a vaccine for either yourself or your child contact your doctor or pediatrician to get more information about the specific vaccine that you’re concerned with. We want only the best for you and your child and understanding how vaccines work is imperative in making the best choices for you and your family. 


Cleveland Clinic. (2021, March 18). Vaccine FAQs: How Are Vaccines Developed, and How Do They Work? Health Essentials from Cleveland Clinic.

Office of Infectious Disease and HIV/AIDS Policy (OIDP). (2021, April 27). Vaccine Ingredients. HHS.Gov.

Easy-to-read Immunization Schedule by Vaccine for Ages Birth-6 Years | CDC. (2021, February 12). Centers for Disease Control and Prevention.

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