How do COVID-19 vaccines work?

There are currently four vaccines for COVID-19: the Pfizer-BioNTech (Comiranty) vaccine is fully approved for standard use by the U.S. Food and Drug Administration (FDA) for individuals 16 and older, and authorized for emergency use for those aged 6 months-15 years. The Moderna (Spikevax) vaccine is fully approved for standard use for individuals 18 years and older, and authorized for emergency use for those aged 6 months-17 years. The Johnson & Johnson (Janssen) and Novavax vaccines are also authorized for emergency use.    

All of these vaccines are very effective at preventing severe disease and hospitalization. 

In certain types of emergencies, the Food and Drug Administration (FDA) can issue an emergency use authorization (EUA) to provide more timely access to drugs, diagnostic tests, or other critical medical products that may help during an emergency, like the COVID-19 pandemic.

Learn more about EUAs in this video

Watch Pat Winokur, MD, executive dean for the Carver College of Medicine and principal investigator for UI Health Care’s Pfizer-BioNTech COVID-19 vaccine clinical trial, explain what an mRNA vaccine (like Moderna or Pfizer-BioNTech [Comiranty]) is and how it protects your body against the coronavirus:

Early indications are that mild to moderate flu-like side effects might occur, such as arm pain, headache, fatigue, fever, or chills, lasting up to 48 hours. This is your body creating a response to the vaccine and is normal.

We anticipate that this will be the case, though we are waiting for the data from studies to prove that the vaccine reduces spread of disease from person to person.

Learn more about COVID-19 vaccines for children

It typically takes two weeks after vaccination for the body to build protection (immunity) against the virus that causes COVID-19. That means it is possible a person could still get COVID-19 before or just after vaccination because the vaccine did not have enough time to provide protection. People are considered fully protected two weeks after the final dose in their primary vaccine series. _{Source: CDC}

Learn why getting the second dose of your COVID-19 vaccination matters

Watch Melanie Wellington, MD, PhD, explain how you’re still protected from COVID-19 even if you didn’t experience side effects from the vaccination:

People who completed all of the recommended doses of a COVID-19 vaccine which is listed for emergency use by the World Health Organization (WHO) but is not approved or authorized by FDA, or people who completed a heterologous (mix and match) series composed of any combination of FDA-approved, FDA-authorized, or WHO emergency use listed COVID-19 vaccines are considered fully vaccinated and are eligible to receive booster doses. 

Learn more about COVID-19 vaccines that are listed for emergency use by WHO