All About the COVID Vaccines

What are the Ingredients in the COVID-19 Vaccines?

Johnson & Johnson

The active ingredient in Johnson & Johnson (Janssen's) COVID-19 vaccine is a recombinant, replication-incompetent Ad26 vector, encoding a stabilized variant of the SARS-CoV-2 Spike (S) protein.  

This vaccine also includes the following inactive ingredients:

  • polysorbate-80  
  • 2-hydroxypropyl-beta-cyclodextrin  
  • citric acid monohydrate 
  • trisodium citrate dihydrate 
  • sodium chloride 
  • ethanol

Fact Sheet - Johnson & Johnson (Janssen) English and Johnson & Johnson (Janssen) Spanish

April 24 Updated information on the Johnson & Johnson COVID-19 vaccine


The Pfizer BioNTech COVID-19 vaccine includes the following ingredients: 

  • messenger ribonucleic acid (mRNA) 
  • 4 lipid (fatty acid) compounds (for the full list of included lipids, please see the FDA's EUA fact sheet for Pfizer)
  • potassium chloride  
  • monobasic potassium phosphate, 
  • sodium chloride, 
  • dibasic sodium phosphate dihydrate
  • sucrose

Fact Sheet - Pfizer English and Pfizer Spanish


The Moderna COVID-19 vaccine includes the following ingredients: 

  • messenger ribonucleic acid (mRNA) 
  • 4 lipid (fatty acid) compounds (for the full list of included lipids, please see the FDA's EUA fact sheet for Moderna)
  • tromethamine  
  • tromethamine hydrochloride  
  • acetic acid 
  • sodium acetate 
  • sucrose

Fact sheets - Moderna English and Moderna Spanish

Frequently Asked Questions

Does the Johnson & Johnson (Janssen) vaccine cause blood clots?

On April 13, the Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC) recommended a pause in the use of the Johnson & Johnson (Janssen) COVID-19 vaccine due to six reported U.S. cases of a rare and severe type of blood clot in combination with low levels of blood platelets in individuals after receiving the vaccine.

On April 23, the U.S. Food and Drug Administration (FDA) lifted its pause on the use of the Johnson & Johnson vaccine, following a review by a federal vaccine safety review panel.

On April 24, the Western States Scientific Safety Review Workgroup concluded the Johnson & Johnson vaccine is safe and effective and recommended resuming use of the vaccine for all eligible Californians.

Updated information on the Johnson & Johnson COVID-19 vaccine

Learn more about what this means on the Shot of Prevention website.

Can people with underlying medical conditions receive the vaccine?

COVID-19 vaccines may be administered to people with underlying medical conditions if they have not had a severe or immediate (even if it was not severe) allergic reaction to any of the ingredients in the vaccine.

Patients should inform their vaccination provider about their allergies and health conditions. For more information about COVID-19 vaccines and allergic reactions, visit the CDC website.

What are the vaccine contraindications?

CDC considers a history of the following to be a contraindication to vaccination with COVID-19 vaccines: 

  • Severe allergic reaction (e.g., anaphylaxis) after a previous dose or to a component of the COVID-19 vaccine.
  • Immediate allergic reaction of any severity to a previous dose or known (diagnosed) allergy to a component of the vaccine. 

People with a contraindication to one of the mRNA COVID-19 vaccines should not receive doses of either of the mRNA vaccines (Pfizer-BioNTech or Moderna). However, people with a contraindication to mRNA COVID-19 vaccines may be able to receive Janssen COVID-19 vaccine, and vice versa, provided certain measures are taken. As a change from previous versions of the guidance, known polysorbate allergy is no longer a contraindication to mRNA vaccination, however, known polysorbate allergy is a contraindication to Janssen COVID-19 vaccine and thus, a precaution to mRNA COVID-19 vaccination. 

CDC considers a history of an immediate allergic reaction to any other vaccine or injectable therapy (i.e., intramuscular, intravenous, or subcutaneous vaccines or therapies [excluding subcutaneous immunotherapy for allergies, i.e., “allergy shots”]) as a precaution but not a contraindication to vaccination. People with a reaction to a vaccine or injectable therapy that contains multiple components, one of which is a vaccine component, but in whom it is unknown which component elicited the immediate allergic reaction, have a precaution to vaccination. 

Please note that the information provided above is based on CDC’s current interim clinical considerations regarding COVID-19 vaccines and other resources. Information about COVID-19 vaccines is rapidly evolving. Please check back regularly for updated information.