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How do COVID-19 vaccines work?

Last Updated: 02/15/2023

Vaccines work by triggering a person's immune system to develop protection against a disease.

COVID-19 vaccines help our bodies develop immunity to the virus that causes COVID-19 without us having to get the illness. Different types of vaccines work in different ways to offer protection.

mRNA Vaccines

The Pfizer-BioNTech and Moderna vaccines, two of the vaccines currently being administered in New Jersey, are messenger RNA vaccines (mRNA).

Unlike many other vaccines that put a weakened or inactivated germ into our bodies, mRNA vaccines when injected instruct our cells how to make a protein—or even just a piece of a protein—that triggers an immune response inside our bodies. That immune response, which produces antibodies, is what protects us from getting infected if the real virus enters our bodies.

Both vaccines are given as an injection into the muscle and as a series of two shots. The Pfizer-BioNTech vaccine is two doses given 21 days apart and the Moderna vaccine is two doses given 28 days apart.

This is the first time that mRNA vaccines have been distributed to the public, but researchers have been studying and working with mRNA vaccines for decades. Interest has grown in these vaccines because they can be developed in a laboratory using readily available materials. This means the process can be standardized and scaled up, making vaccine development and production faster than traditional methods of making vaccines.

As soon as the necessary information about the virus that causes COVID-19 was available, scientists began designing the mRNA vaccine for cells to build the unique spike protein into an mRNA vaccine.

Receiving an mRNA vaccine will not alter your DNA. mRNA (messenger ribonucleic acid) can most easily be described as instructions for how to make a protein or even just a piece of a protein. mRNA is not able to alter or modify a person's genetic makeup (DNA).

For more of how COVID-19 mRNA vaccines work, visit this CDC page.

Viral Vector Vaccines

Johnson & Johnson's Janssen vaccine is a viral vector vaccine.

Viral vector vaccines use a modified version of a different virus (the vector) to deliver important instructions to our cells. For COVID-19 viral vector vaccines, the vector (not the virus that causes COVID-19, but a different, harmless virus) will enter a cell in our body and then use the cell's machinery to produce a harmless piece of the virus that causes COVID-19. This piece is known as a spike protein and it is only found on the surface of the virus that causes COVID-19.

Scientists began creating viral vectors in the 1970s. Besides being used in vaccines, viral vectors have also been studied for gene therapy, to treat cancer, and for molecular biology research. Some vaccines recently used for Ebola outbreaks have used viral vector technology, and a number of studies have focused on viral vector vaccines against other infectious diseases such as Zika, flu, and HIV.

For more on how COVID-19 viral vector vaccines work, visit this CDC page.

Protein Subunit Vaccines

The Novavax COVID-19 vaccine, one of the vaccines currently available in the United States, is a protein subunit vaccine.

Protein subunit vaccines contain pieces (proteins) of the virus that causes COVID-19. These virus pieces are the spike protein. After vaccination, nearby cells pick up these proteins and our immune system recognizes these proteins do not belong there. Another ingredient in the vaccine, the adjuvant, helps our immune system produce antibodies and activate other immune cells to fight off what it thinks is an infection.

At the end of the process, our bodies have learned how to respond to the spike protein, and our immune system will be able to respond quickly to the actual virus spike protein and protect you against COVID-19.

Protein subunit vaccines have been used for years. More than 30 years ago, a hepatitis B vaccine became the first protein subunit vaccine to be approved for use in the United States. Whooping cough vaccines are another example of commonly used protein subunit vaccines.

For more on how COVID-19 protein subunit vaccines work, visit this CDC page.

Additional information on other COVID-19 vaccines that are or soon will be undergoing large-scale (Phase 3) clinical trials in the United States can be found here.

For more information about COVID-19 vaccine safety, side effects, and how they were tested and approved, refer to this article.

Sources: NJ DOH COVID-19 Vaccine FAQs, NJ DOH COVID-19 Vaccines - Know the Facts, CDC;; DOH Commissioner Remarks (2/8/21)