Vaccines work by teaching your body's immune system to recognize and fight back against germs, such as a virus, that can cause serious illness. By getting vaccinated, you develop protection against a dangerous illness without having to get sick.

What is an mRNA vaccine?

The Moderna and Pfizer vaccines are messenger RNA vaccines, also called mRNA vaccines. They contain genetic material or "instructions" that teach cells in your body to make a harmless piece of spike protein. That piece of protein, in turn, tells your immune system to produce the antibodies needed to protect you. After the piece of protein is made, the cell breaks down the instructions and gets rid of them.

How long have researchers been studying mRNA vaccines?

The three COVID-19 vaccines currently available in the U.S. use technology that researchers at the National Institutes of Health have been studying for decades. This technology can fight the spike proteins that stick out from the surface of the COVID-19 virus.

What is a viral vector vaccine?

The Johnson & Johnson vaccine, which is a viral vector vaccine, works in a similar way. Instead of RNA, it carries a slightly different version of another virus than the one that causes COVID-19. This different virus, called a "viral vector," carries the same type of important instructions that mRNA vaccines do. Once the instructions are inside your cells, they tell them to make a harmless piece of spike protein, which then triggers your immune system to make protective antibodies.

Can the COVID-19 vaccines give you COVID-19?

The COVID-19 vaccines cannot give you COVID-19. The symptoms that sometimes come after you've had a vaccine shot are normal and a sign that your immune system is working. Call your health care provider or 911 if you are concerned about an allergic or other reaction, which is very rare.

How do I know if I'm fully vaccinated?

People are considered fully vaccinated two weeks after their second shot in a two-dose series, like the Pfizer or Moderna vaccines, or two weeks after a single-shot vaccine, like the Johnson & Johnson vaccine.

Where can I learn more about getting a COVID-19 vaccine?

Visit vaccines.gov or your local state health website to learn where and when you can get a COVID-19 vaccine. If you have more questions about the COVID-19 vaccine, visit the Centers for Disease Control and Prevention website and talk to your health care provider.