A year into the pandemic, groundbreaking new vaccines that prime the body to fight against the virus that causes coronavirus disease (COVID-19) are a critical step toward stopping the spread of the virus and protecting millions at risk of severe illness.

The Pfizer–BioNTech and Moderna vaccines are the first to receive emergency use authorization by the U.S. Food and Drug Administration (FDA). In clinical trials, both were found to be highly effective—around 95 percent—in preventing COVID-19. 

The two share another impressive trait: unlike traditional vaccines that have been effectively used for decades against diseases such as measles and polio, they do not contain a weakened or inactive form of the virus itself. Instead, they use messenger RNA (mRNA) to teach the immune system to recognize and react to a component of the virus that is key to its ability to make us sick. This is a major advance in public health and vaccine development.

“This is the first time in history we’ve had an mRNA vaccine available widely to the public,” says Mark J. Mulligan, MD, director of both the Division of Infectious Diseases and Immunology and NYU Langone’s Vaccine Center, which was involved in COVID-19 vaccine clinical trials. “This is an exciting development because it provides us with a new way to develop vaccines that have the potential to save thousands of lives.”  

Defending the Body Against COVID-19

Viruses can’t reproduce themselves. They need a host. The coronavirus uses a spike protein to gain entry into the cells and start the replication process that makes us sick. In developing mRNA vaccines, scientists zeroed in on a unique spike protein that is found on the surface of the virus. On its own, this spike protein is incapable of causing COVID-19. The mRNA vaccines work by relaying a set of instructions for how to build this protein, with the goal of teaching your immune system how to disarm it.

After injection, the vaccine particles come into contact with immune system cells and deliver the mRNA message: you need to make this spike protein, and here’s how. As the vaccinated cells start churning out the spike protein, other immune system cells realize that the protein should not be there. That’s when the battle begins.

“The immune system starts building an immune response and making antibodies,” says Aisha Langford, PhD, MPH, assistant professor in NYU Langone’s Department of Population Health. “And that’s how we train the immune system to recognize the spike protein, and that’s what protects us from being infected.”

Your body continues to produce antibodies until all the spike proteins have been destroyed. At the end of this natural immune process, your immune system has the knowledge it needs to recognize the spike protein and fend off future exposure to the virus. So if the virus enters the body, the immune system will identify and attack it.

Reactions after receiving the vaccine, such as headaches, chills, joint pain, and muscle soreness at the injection site, are normal and expected. “These are not allergic reactions, but actually a sign that the vaccine is producing an immune response,” says Michael S. Phillips, MD, NYU Langone’s chief epidemiologist.

The mRNA vaccines do not enter the nucleus of the cell, so it cannot change your DNA. After the mRNA delivers instructions to your cells, the body breaks it down and eliminates it. 

NYU Langone is distributing the COVID-19 vaccines to our patients, based on federal and state eligibility guidelines and the available vaccine supply. While patients are not able to choose which vaccine they receive, both mRNA vaccines are highly protective and require two doses: the first develops the immune response, and the second strengthens it. 

At this time, the vaccine is also the best way to protect not only ourselves but those who are most vulnerable to the disease.

“A vaccine provides protection for me, but it’s also a social act, an altruistic act, where we protect others,” says Dr. Mulligan. “Even if you don’t feel like you need it, it’s important for our community that we all receive it.”