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COVID-19 Vaccine Glossary

Vaccine information continues to evolve and you may hear new words or phrases that are unfamiliar. Learn more about some of the terms associated with these vaccines.


Adenoviruses are a group of viruses that typically spread through a cough or sneeze, or through close contact with others. They cause illnesses such as bronchitis and pneumonia.


Antibodies are proteins made by your body’s immune system that appear in your body after you’ve been infected with a virus or other germs, such as COVID-19, and they can help fight off the illness if you become infected again. However, it’s not clear how long antibodies last after patients recover from COVID-19, which is why it’s important to get vaccinated, even if you’ve already had the virus.

Antigen test

An antigen test, also known as a rapid test, detects fragments of proteins from COVID-19. This kind of test, which can help determine whether someone has the virus, is quicker than other tests, but may not be as accurate.

Emergency use authorization

During a public health emergency, like the COVID-19 pandemic, the FDA can issue fast-tracked approvals of drugs like the COVID-19 vaccines. The process is different from the normal FDA approval process, but that does not mean that the drugs approved for Emergency Use Authorization are unsafe.

Herd immunity

When a significant portion of the population is immune from an infectious disease, the spread of the disease cannot spread as easily in the population. “Herd immunity” can help to protect people who cannot be vaccinated, such as newborn babies. However, it is not a replacement for a vaccine. Vaccination is the fastest way to develop herd immunity.

mRNA vaccines

The Pfizer and Moderna COVID-19 vaccines are mRNA vaccines. They consist of genetic material called messenger RNA, or mRNA, that guides the body’s cells to make proteins, which then cause the immune system to make antibodies that protect against COVID-19.

Spike protein

Spike proteins are the proteins that surround the COVID-19 virus and stick to human cells during infection. mRNA vaccines guide the body to make the spike protein, allowing the body to create antibodies to fight the virus.

Vaccine passport

The term vaccine passport refers to a document that proves someone has gotten their COVID-19 vaccine. However, this is currently not a requirement in the U.S.


V-safe is an online tool that allows you to report to the CDC any side effects you may experience after getting your COVID-19 vaccine. The CDC uses this information to monitor the vaccine’s safety. Sign up for V-safe.

Viral vector vaccines

Viral vector vaccines use a modified version of a virus to enter the cells, allowing the body to create antibodies. These vaccines do not use COVID-19 and cannot give you the virus, or alter your DNA. The virus used is “attenuated,” meaning it does not cause disease, or “replication incompetent,” meaning that it is unable to reproduce and therefore cannot cause disease.

Learn more about COVID-19 vaccines