Understanding mRNA COVID-19 Vaccines

The Pfizer-BioNTech and Moderna COVID-19 vaccines are messenger RNA vaccines also called mRNA vaccines. mRNA vaccines are some of the first COVID-19 vaccines authorized and approved for use in the United States.

How mRNA Vaccines Work

To trigger an immune response, many vaccines put a weakened or inactivated germ into our bodies. Not mRNA vaccines. Instead, mRNA vaccines use mRNA created in a laboratory to teach 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.

1. First, COVID-19 mRNA vaccines are given in the upper arm muscle. The mRNA will enter the muscle cells and instruct the cells’ machinery to produce a harmless piece of what is called the spike protein. The spike protein is found on the surface of the virus that causes COVID-19. After the protein piece is made, our cells break down the mRNA and remove it.
2. Next, our cells display the spike protein piece on their surface. Our immune system recognizes that the protein doesn’t belong there. This triggers our immune system to produce antibodies and activate other immune cells to fight off what it thinks is an infection. This is what your body might do to fight off the infection if you got sick with COVID-19.
3. At the end of the process, our bodies have learned how to protect against future infection from the virus that causes COVID-19. The benefit of COVID-19 mRNA vaccines, like all vaccines, is that those vaccinated gain this protection without ever having to risk the potentially serious consequences of getting sick with COVID-19. Any temporary discomfort experienced after getting the vaccine is a natural part of the process and an indication that the vaccine is working.

COVID-19 mRNA Vaccines Have Been Rigorously Evaluated for Safety

mRNA vaccines have been held to the same rigorous safety and effectiveness standardsexternal icon as all other types of vaccines in the United States. The only COVID-19 vaccines the Food and Drug Administration (FDA) makes available for use in the United States (by approval or emergency use authorization) are those that meet these standards.

mRNA Vaccines Are Newly Available to the Public But Have Been Studied for Decades

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 vaccines can be developed and produced in large quantities faster than with other methods for making vaccines.

mRNA vaccines have been studied before for flu, Zika, rabies, and cytomegalovirus (CMV). As soon as the necessary information about the virus that causes COVID-19 was available, scientists began designing the mRNA instructions for cells to build the unique spike protein into an mRNA vaccine.

Future mRNA vaccine technology may allow for one vaccine to provide protection against multiple diseases, thus decreasing the number of shots needed for protection against common vaccine-preventable diseases.

Beyond vaccines, cancer research has used mRNA to trigger the immune system to target specific cancer cells.