• Elijah Davis

What's in the Pfizer and Moderna Vaccines?

Updated: Mar 23, 2021

Since its declaration as a global pandemic in March 2020, Coronavirus Disease 2019 (COVID-19) has taken the world by storm. In the United States alone, tens of millions of people have felt the wide-reaching effects of this pandemic. Not only do they face health-related issues, but financial instability and mental health troubles well. Scientists and clinicians around the globe are working to develop measures to protect against infection and resolve these challenges.

The end of 2020 saw the rapid development of several promising vaccines. The first two of these candidates to have been cleared for Emergency Use Authorization (EUA) by the Food and Drug Administration are BNT162b2 (by Pfizer-BioNTech) and mRNA-1273 (by ModernaTX, Inc). Clinical trials conducted found the effectiveness of these vaccines to be 95% and 94.1%, respectively. To date, these are the leading vaccines in preventing infection in the United States.

Unfortunately, the challenge is not just in creating a protective vaccine. Health officials must also get them into the hands and, more importantly, the immune systems of the general public. There is much hesitation within many communities when determining if they would accept either vaccination. Many point out a lack of knowledge of what exactly is in the vaccine. Using the FDA-approved fact sheets provided by Moderna and Pfizer, we have provided an overview of the vaccine’s ingredients and functions.

Genetic Material – Active Ingredient

Usually, conventional vaccines use inactivated or weakened viral particles. However, both Pfizer’s and Moderna’s vaccines use messenger RNA (mRNA) as the active ingredient. This mRNA serves as a genetic template for the virus’s spike protein. These spikes allow the virus to bind to cellular receptors and infect the cell.

Administration of this mRNA causes cells to produce the spike protein without the virus itself. The protein is then recognized as foreign material by the immune system. The body proceeds to make antibodies against the spike protein, along with immune cells able to recognize and respond to it. As a result, if the virus enters the body, the circulating antibodies will bind to it and prevent it from attaching to and infecting the human cells. Additionally, these antibodies act as a signal for immune cells to eliminate the virus.

There are concerns that the mRNA in these vaccines can modify our DNA or produce infectious viral particles. The use of mRNA to generate protein is a basic biological function common to all forms of life. As a rule, mRNA cannot travel to the nucleus of a cell and be converted into DNA. mRNA is transient - it has a short life within cells. Cells contain multiple factors that bind to mRNA and break it down to recycle its’ components. While the mRNA may be short-lived, the antibodies and cell-specific response last a while. Lastly, the mRNA only carries code for a piece of the virus. It cannot produce the entire virus, as it does not contain the blueprint for that.

Lipids (Fats) – Transport System

Lipids help stabilize the mRNA as it enters cells and protects it from early destruction. They form a coating around the genetic material, also called a lipid bubble. Much like mRNA, lipid molecules are naturally present within the body. After helping to transport the mRNA, the lipids are dissolved and removed from the body.

Salts – Vaccine Buffer Balance

Salts are used to balance the pH of the vaccine’s liquid component. They are also called buffers and they keep the vaccines similar to what is found within the body. This prevents the body from trying to eliminate the vaccine.

Sucrose – Stabilization

While many know sucrose as a delicious sugar molecule found in table sugar and most fruits, it has several important properties that aid in vaccine development. It acts to stabilize vaccines during the freezing and thawing process, protecting the other ingredients from breaking down. Sucrose also keeps the vaccine’s liquid composition close to what is found in the body.

Acids and Acid Stabilizers (Moderna Only)

Much like salt, acids and acid stabilizers act to adjust pH of the vaccine’s liquid buffer component. They also play a role in maintaining the stability of the vaccine.

Together, these ingredients make for a powerful and safe tool to fight COVID-19. Health officials do advise noting any allergies against these components, as they can be responsible for adverse reactions.


Speaking Plainly:

  • The main ingredient in both Pfizer and Moderna vaccines is mRNA, which helps the body to make the spike protein alone, and not the entire virus.

  • The spike protein is the part of the virus that allows it to infect human cells.

  • The body identifies the spike protein as foreign material and creates antibodies and immune cells that attack it.

  • If the body is infected by the real virus, the antibodies are already present to attack it, prevent it from entering the cells, and eliminate it from the body.

  • The other ingredients in both vaccines are lipids, salts, sucrose, and Moderna has acids and acid stabilizers.