COVID-19 vaccines: How do they work?

October 20, 2021

By Teena Chopra, M.D., M.P.H., Division of Infectious Disease

All COVID-19 vaccines currently available in the United States are effective at preventing COVID-19 and have proven to be safe and effective.

The Pfizer and Moderna vaccines (2 doses) are made using messenger RNA, or mRNA, a technology that delivers a bit of genetic code to cells — in effect, a recipe to make the surface protein (known as “spike”) on the SARS-2 virus. The proteins made with the mRNA instructions activate the immune system, teaching it to see the spike protein as foreign and develop antibodies and other immunity weapons with which to fight it.

The J&J vaccine (1 dose) uses a different approach to instruct human cells to make the SARS-2 spike protein.  It is what’s known as a viral-vectored vaccine. A harmless adenovirus has been engineered to carry the genetic code for the SARS-2 spike protein. Once the adenovirus enters cells, they use that code to make spike proteins.

To trigger an immune response, many vaccines put a weakened or inactivated germ into our bodies. On the other hand, COVID-19 vaccines give instructions for our cells to make a HARMLESS piece of what is called the “spike protein.”  This spike protein is also found on the surface of the virus that causes COVID-19.

First, COVID-19 mRNA vaccines are given in the upper arm muscle. Once the instructions are inside the muscle cells, the cells use them to make the protein piece.  Next, the cell displays the protein piece on its surface. Our immune systems recognize that the protein doesn’t belong there and begin building an immune response and making antibodies, like what happens in natural infection against COVID-19.

At the end of the process, our bodies have learned how to protect against future infection. The benefit of COVID-19 vaccines, like all vaccines, is those vaccinated gain this protection without ever having to risk the serious consequences of getting sick with COVID-19.

Booster shot:

The FDA recently issued an emergency use authorization (EUA) for the Pfizer-BioNTech COVID-19 Vaccine which allows for the use of a single booster dose, to be administered at least six months after completion of the primary series.  This applies to the following: individuals 65 years of age and older; individuals 18 through 64 years of age at high risk of severe COVID-19; and individuals 18 through 64 years of age whose frequent institutional or occupational exposure to SARS-CoV-2 puts them at high risk of serious complications of COVID-19 including severe COVID-19.

The Delta variant:

 The Delta variant causes more infections and spreads faster than earlier forms of the virus that causes COVID-19. It might cause more severe illness than previous strains in unvaccinated people.  Vaccines continue to reduce a person’s risk of contracting the virus that causes COVID-19, including this variant.  Vaccines continue to be highly effective at preventing hospitalization and death, including against this variant.

The Wayne Health Mobile Unit is a great place to get your vaccine and other preventative health care. Wayne Health Mobile Units are staffed by registered nurses, medical/research assistants, community health workers, patient & family health advocates, and overseen by physicians from the Center of Population Health and Accountability at Wayne Health. Our team offers a variety of free health screenings and services to our patients.  Mobile units deliver an ever-expanding menu of health services directly to your neighborhood or place of employment.

Things to remember when getting the vaccine:

  • You CANNOT catch COVID-19 from these vaccines: these vaccines DO NOT use the live virus that causes COVID-19.
  • COVID-19 vaccines have been held to the same rigorous safety and effectiveness standards as all other types of vaccines in the United States. The only COVID-19 vaccines the Food and Drug Administration (FDA) will make available for use in the United States (by approval or emergency use authorization) are those that meet these standards.
  • Possible side effects: fever (39°C to 40°C or 102.2 °F to 104°C), muscle pain, joint pain, headache, nausea and fatigue.

Learn more about the Wayne Health Mobile Unit and view the event calendar.

To make an appointment with a Wayne Health provider, visit our appointment page or call (877) 929-6342.

COVID-19 vaccines: How do they work?

Back to News & Media