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April 24, 2021

How COVID-19 vaccines work

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All adults are now eligible to receive a COVID-19 vaccine in Missouri and Kansas. If you haven’t gotten vaccinated yet and live in Missouri, make an appointment today.  And if you’re still unsure if you want to get vaccinated for COVID-19, read on for information compiled by Dr. Letoia Clark, a pharmacist doing her residency at KC CARE.

How do vaccines work?

When germs, such as the virus that causes COVID-19, invade our bodies, they attack and multiply. This invasion, called an infection, is what causes illness.  The first time a person is infected with the virus that causes COVID-19, their immune system makes and uses germ-fighting tools to get over the infection.

After the infection, the person’s immune system remembers what it learned about how to protect the body against that virus. If the body encounters the same virus again, defensive white blood cells quickly go into action and antibodies are produced.

Pfizer-BioNTech and Moderna are types of mRNA vaccines which contain protein material that our bodies recognize as foreign. Our bodies then produce defensive white blood cells that will remember how to fight the virus that causes COVID-19 if we are infected in the future.

Johnson & Johnson’s Janssen vaccine is classified as a viral vector vaccine. It contains modified versions of a different virus than the one that causes COVID-19. Inside the shell of the modified virus is material that gives cells instructions to make a protein unique to the virus that causes COVID-19. The protein is then copied to allow our bodies to build defensive white blood cells, which will remember how to fight that virus if we are infected in the future.

Comparing COVID-19 Vaccines Available in the U.S.

All authorized and recommended COVID-19 vaccines are safe, effective (>66%), and reduce the risk of severe illness. They do not use the live virus that causes COVID-19; therefore, they cannot give someone COVID-19. Additionally, these vaccines do not affect or interact with our DNA in any way.

Who can get this vaccine? How many doses do I need? When will it be fully effective?
Pfizer-BioNTech People 16 years and older Two doses, 21 days apart Two weeks after 2nd shot
Moderna People 18 years and older Two doses, 28 days apart Two weeks after 2nd shot
Johnson & Johnson 

or Janssen

People 18 years and older One dose Two weeks after shot


Note: The CDC does not recommend one vaccine over the others. 

The best COVID-19 vaccine is the first one that is available to you.


We want to hear from you. 

Are you and your loved ones still nervous to get a COVID-19 vaccine? Tell us why by completing our our survey.


  1. Coronavirus Disease 2019 (COVID-19). Centers for Disease Control and Prevention. https://www.cdc.gov/coronavirus/2019-ncov/index.html. Published 2021.