How Vaccines Work

MUSC Health
March 04, 2021
For more than 220 years, life-saving vaccines have been used to eradicate deadly diseases.

For more than 220 years, life-saving vaccines have been used to eradicate deadly diseases. From smallpox and measles to polio and tetanus, vaccines have saved lives, improved quality of life, and been a mainstay of public health.

As the United States enters the second year in the battle against a deadly pandemic, there is hope on the horizon. The rollout of the Pfizer-BioNtech and Moderna vaccines, along with the prospect of others receiving emergency approval, are a major step toward controlling the pandemic.

"The COVID vaccines are the most effective tool we have to reach herd immunity and protect all of us against COVID-19,” says Dr. Krutika Kuppalli, Assistant Professor of Medicine in MUSC's Division of Infectious Diseases. "Vaccines work with our body's immune system to build protection against a deadly germ without us getting sick. They're a safe way to reduce our risk of getting a disease."

Dr. Kuppalli says once you get vaccinated, your body recognizes the invading germs -- virus or bacteria -- that are part of the vaccine as "foreign." Your immune system produces proteins, or antibodies, to fight the disease and trains those antibodies to recognize the disease and remember how to fight it. Thus, if you're exposed to the germ again, your immune system can destroy it quickly to prevent you from getting sick.

Many COVID-19 vaccines are being developed, but three types that have received attention are genetic mRNA vaccines, viral vector vaccines and protein-based vaccines.

The Pfizer-BioNtech and Moderna vaccines rely on mRNA technology, whereas the AstraZeneca and Johnson & Johnson vaccines use viral vector technology. Both prompt the body's cells to create a piece of the spike protein.

"mRNA vaccines give instructions for our cells to make a harmless piece of the spike protein, which is found on the surface of the coronavirus," Dr. Kuppalli says. "The vaccine is given in the upper arm muscle, and once the mRNA instructions are inside the cells, the cells use them to make the piece of the spike protein. After this is made, the cell breaks down the instructions.

"Next, the cell displays the piece of the spike protein on its surface. Our immune system recognizes the protein as foreign and develops an immune response by making antibodies, which is the same process that occurs in natural infection against COVID-19. When the process is complete, our bodies have learned how to protect against future infection."

The Moderna and Pfizer-BioNTech vaccines require two doses 28 and 21 days apart respectively.

The Johnson & Johnson vaccine, which will be reviewed later this month by the Food and Drug Administration, is a single dose and uses the viral vector technology. With these types of platforms, the gene for the coronavirus spike protein is delivered to human cells after being inserted into a harmless adenovirus. The spike protein is produced in the cells and prompts an immune response to produce antibodies.

Protein-based vaccines are a third type of vaccine in development. These vaccines contain specific pieces of the coronavirus proteins but no genetic material. Many common vaccines, such as the pneumonia (pneumococcal) vaccines, are protein-based.

After the genetic code for Severe Acute Respiratory Syndrome Coronavirus - 2 SARS-CoV2, the virus that causes COVID-19, was made available in early January 2020, scientists around the world began working on a vaccine immediately, Dr. Kuppalli says.

"Moreover, scientists were able to leverage prior knowledge and research gained from other coronavirus infections such as Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS)," Dr. Kuppalli says.

For ongoing updates, please visit our Coronavirus Information page.

About the Author

MUSC Health

Keywords: COVID-19