Know How COVID-19 Vaccines Work

Each of the COVID-19 vaccines is designed to teach the body how to recognize the COVID-19 virus. The vaccine does this by stimulating an immune response to the spike protein found on the surface of the SARS-CoV-2 virus.

It is important to be clear that COVID-19 vaccines do not and cannot cause COVID-19 infection. These vaccines do not alter the body’s DNA. Let the patient know that they might experience a fever, headache, or chills within the first few days after receiving the vaccine; this is the body’s response to the vaccine that means it’s working! If a patient does not experience these symptoms, it doesn’t necessarily mean that they did not develop immunity. Everyone reacts differently.

How the vaccine stimulates this immune response varies with the type of vaccine, or vaccine platform, that is used. Several types of vaccine platforms are being used or studied for COVID-19. Click on each type of vaccine below to learn how it works and access information for patients.

mRNA Vaccines

How They Work

These vaccines deliver short segments of messenger RNA (mRNA) with instructions that tell your body how to recognize and fight off the COVID-19 virus in the future.

The Pfizer-BioNTech and Moderna COVID-19 vaccines are mRNA vaccines.

The Steps

  1. An mRNA vaccine delivers a short segment of mRNA that act as a temporary blueprint with instructions that tell your immune cells how to make the COVID-19 spike protein on your own. This step is specific for mRNA vaccines.
  2. Your immune cells take the spike protein and display it on their cell surfaces to tell the body to learn to recognize spike proteins as intruders, thus building your immunity against the COVID-19 virus. This step is similar to the way other vaccines work.
  3. Your immune cells break down the mRNA into amino acids within a few hours.
  4. If the person is infected with COVID-19 in the future, your body’s immune system will recognize the spike protein and know to attack it to reduce your chance of COVID-19 disease.

Learn More

Print for Patients

Share CDC’s How mRNA COVID-19 Vaccines Work (Spanish): a printable poster for patients that provides an overview of the mechanism of action.

Viral Vector Vaccines

How They Work

Viral vector vaccines deliver a harmless virus that tells your body how to recognize and fight off the COVID-19 virus.

The Johnson & Johnson/Janssen COVID-19 vaccine is a viral vector vaccine.

The Steps

  1. You may recall that when a “bad” virus infects the body, it enters your body’s cells and hijacks the cellular machinery to make more of itself, or replicate. Instead, viral vector vaccines deliver a “good” virus that harnesses the cellular machinery to make the COVID-19 spike protein. This viral vector was designed so that it cannot replicate.
  2. The “good” virus in the case of the Johnson & Johnson/Janssen COVID-19 vaccine is an adenovirus. This adenovirus is strong enough to enter a cell and deliver a short gene segment that provides instructions for how to create the COVID-19 spike protein. These vaccines do not change nor join into a person’s DNA; they just tell the body how to temporarily make a protein using DNA.
  3. Your immune cells make the spike protein and display it on their cell surfaces to tell the body to learn to recognize spike proteins as intruders, thus building your immunity against the COVID-19 virus. This step is similar to the way other vaccines work.
  4. If the person is infected with COVID-19 in the future, your body’s immune system will recognize the spike protein and know to attack it to reduce your chance of COVID-19 disease.

Learn More

Print for Patients

Share CDC’s How Viral Vector COVID-19 Vaccines Work (Spanish): a printable poster for patients that provides an overview of the mechanism of action.

Protein-based Vaccines

How They Work

These vaccines deliver protein fragments of the COVID-19 spike protein to tell your body how to recognize and fight off the COVID-19 virus.

The Novavax COVID-19 vaccine is a protein-based vaccine in development.

Inactivated Vaccines

How They Work

These vaccines use chemicals to kill the virus, so the virus can’t multiply. Then, the inactivated virus is injected to train your body to recognize and fight off the virus.

There are currently no inactivated COVID-19 vaccines in development in the United States to fight against COVID-19.