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Understanding Viral Vector COVID-19 Vaccines

What You Need to Know

  • Viral vector vaccines use a “vector virus,” which is a harmless, modified version of a virus that does not cause COVID-19.

  • The vector virus delivers important instructions to our cells on how to recognize and fight the virus that causes COVID-19.

  • Researchers have been studying and working with viral vector vaccines for decades.

  • Like all vaccines, viral vector vaccines benefit people who get vaccinated by giving them protection against diseases like COVID-19 without them having to risk the potentially serious consequences of getting sick.

Johnson & Johnson’s Janssen COVID-19 vaccine is a viral vector vaccine. Learn more about Johnson & Johnson’s Janssen COVID-19 vaccine, including who can get it, doses, and ingredients.

How Viral Vector COVID-19 Vaccines Work

Viral vector COVID-19 vaccines use a modified version of a different virus (a vector virus) to deliver important instructions to our cells.

  1. First, viral vector COVID-19 vaccines are given in a muscle in the upper arm. The vector virus in the vaccine is not the virus that causes COVID-19, but a different, harmless virus. It enters the muscle cells and uses the cells’ machinery to produce a harmless piece of what is called a spike protein. The spike protein is found on the surface of the virus that causes COVID-19. After the spike protein piece is made, our cells break down the vector virus and remove it.

  2. Next, our cells display the spike protein on their surface. Our immune system recognizes that the spike protein does not belong there. This triggers our immune system to produce antibodies and activate other immune cells to fight off what it is an infection. This response is similar to what your body does if you get sick with COVID-19, but is temporary.

  3. At the end of the immune building process, our bodies have learned how to help protect against future infection with the virus that causes COVID-19. People get this protection from a vaccine, without ever having to risk the potentially serious consequences of getting sick with COVID-19. Any side effects from getting the vaccine are normal signs the body is building protection.

Facts About Viral Vector COVID-19 Vaccines

Viral vector COVID-19 vaccines cannot give someone COVID-19 or other illnesses.

  • Viral vector COVID-19 vaccines cannot cause infection with COVID-19 or with the virus used as the vaccine vector.

They do not affect or interact with our DNA.

  • The genetic material delivered by the viral vector does not integrate into a person’s DNA.

Viral Vector Vaccines Have Been Rigorously Studied for Safety

Viral vector COVID-19 vaccines are safe and effective. Viral vector COVID-19 vaccines have been held to the same rigorous safety and effectiveness standards as all other types of vaccines in the United States. The only COVID-19 vaccines the U.S. Food and Drug Administration (FDA) will make available for use in the United States (by approval or emergency use authorization) are those that meet these standards.

While COVID-19 vaccines were developed rapidly, all steps have been taken to ensure their safety and effectiveness.

How Viral Vector Vaccines Have Been Used During Recent Disease Outbreaks

Scientists began creating viral vectors in the 1970s. Besides being used in vaccines, viral vectors have also been studied for gene therapy, to treat cancer, and for molecular biology research. For decades, hundreds of scientific studies of viral vector vaccines have been done and published around the world. Some vaccines recently used for Ebola outbreaks have used viral vector technology, and several studies have focused on viral vector vaccines against other infectious diseases such as Zika, flu, and HIV.

Use CDC’s COVID-19 booster tool to learn if and when you can get boosters to stay up to date with your COVID-19 vaccines. Staying up to date means getting all recommended COVID-19 vaccines including boosters when eligible.

People who are moderately or severely immunocompromised have specific COVID-19 vaccine recommendations, which include a third dose to complete their primary series, as well as two booster doses for those eligible.

Learn More About Viral Vector Vaccines How Viral Vector COVID-19 Vaccines Work

PDF infographic explaining how viral vector COVID-19 vaccines work.

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