Important update: Healthcare facilities
CDC has updated select ways to operate healthcare systems effectively in response to COVID-19 vaccination. Learn more
Given new evidence on the B.1.617.2 (Delta) variant, CDC has updated the guidance for fully vaccinated people. CDC recommends universal indoor masking for all teachers, staff, students, and visitors to K-12 schools, regardless of vaccination status. Children should return to full-time in-person learning in the fall with layered prevention strategies in place.
The White House announced that vaccines will be required for international travelers coming into the United States, with an effective date of November 8, 2021. For purposes of entry into the United States, vaccines accepted will include FDA approved or authorized and WHO Emergency Use Listing vaccines. More information is available here.
Travel requirements to enter the United States are changing, starting November 8, 2021. More information is available here.

Overview of COVID-19 Vaccines

Overview of COVID-19 Vaccines
Updated May 23, 2023
What You Need to Know
  • Vaccine recommendations are based on age, time since last dose, and in some cases, the first vaccine received.
  • People who are moderately or severely immunocompromised have specific recommendations for COVID-19 vaccines.
  • Side effects after a COVID-19 vaccine are common, however severe allergic reactions after getting a COVID-19 vaccine are rare.

Types of COVID-19 Vaccines Available

COVID-19 vaccine vials

Vaccines authorized by the U.S. Food and Drug Administration (FDA) currently include:

These vaccines are given as a shot in the muscle of the upper arm or in the thigh of a young child. COVID-19 vaccine ingredients are considered safe for most people. Nearly all of the ingredients in COVID-19 vaccines are ingredients found in many foods—fats, sugar, and salts. None of the COVID-19 vaccines affect or interact with our DNA and the following are not included in the vaccines:

  • No preservatives such as thimerosal or mercury or any other preservatives.
  • No antibiotics such as sulfonamide or any other antibiotics.
  • No medicines or therapeutics such as ivermectin or any other medications.
  • No tissues such as aborted fetal cells, gelatin, or any materials from any animal.
  • No food proteins such as eggs or egg products, gluten, peanuts, tree nuts, nut products, or any nut byproducts. (COVID-19 vaccines are not manufactured in facilities that produce food products).
  • No metals such as iron, nickel, cobalt, titanium, or rare earth alloys. They also do not have any manufactured products like microelectronics, electrodes, carbon nanotubes or other nanostructures, or nanowire semiconductors.
  • No latex. The vial stoppers used to hold the vaccine also do not contain latex.

After the body produces an immune response, it discards all of the vaccine ingredients, just as it would discard any substance that cells no longer need. This process is a part of normal body functioning.

Dosage: COVID-19 vaccine dose amounts can vary depending on the type of vaccine being given, or due to the recipient’s age.

COVID-19 vaccine doses and timing are different for people who are moderately or severely immunocompromised.

Vaccines for Immunocompromised

Pfizer-BioNTech and Moderna mRNA COVID-19 vaccines

mRNA vaccines use mRNA created in a laboratory to teach our cells how to make a protein—or even just a piece of a protein—that triggers an immune response inside our bodies. The mRNA from the vaccines is broken down within a few days after vaccination and discarded from the body.

Novavax protein subunit COVID-19 vaccine

Protein subunit vaccines contain pieces (proteins) of the virus that causes COVID-19. The virus pieces are the spike protein. The Novavax COVID-19 vaccine contains another ingredient called an adjuvant. It helps the immune system respond to that spike protein. After learning how to respond to the spike protein, the immune system will be able to respond quickly to the actual virus spike protein and protect you against COVID-19.

Johnson & Johnson’s Janssen (J&J/Janssen) viral vector COVID-19 vaccine

J&J/Janssen COVID-19 vaccine has expired and is no longer available for use in the United States as of May 6, 2023.

Viral vector vaccines use a harmless, modified version of a different virus (a vector virus), and not the virus that causes COVID-19. The vector virus delivers important instructions to our cells on how to recognize and fight the virus that causes COVID-19.

How Well COVID-19 Vaccines Work

  • People who are up to date have lower risk of severe illness, hospitalization and death from COVID-19 than people who are unvaccinated or who have not completed the doses recommended for them by CDC.
  • Additional updated COVID-19 vaccine doses can help restore protection that has decreased since previous vaccination.
  • CDC will continue to provide updates as we learn more.

Safety of COVID-19 Vaccines

COVID-19 vaccines have undergone—and will continue to undergo—the most intensive safety monitoring in U.S. history. Evidence from the hundreds of millions of COVID-19 vaccines already administered in the United States, and the billions of vaccines administered globally, demonstrates that they are safe and effective.

Side Effects

  • Side effects that happen within 7 days of getting vaccinated are common but are mostly mild. Sometimes they may affect a person’s ability to do daily activities.
  • Side effects throughout the body (such as fever, chills, tiredness, and headache) are more common after the second dose of a Pfizer-BioNTech, Moderna, or Novavax COVID-19 vaccine.

Adverse Events

  • Severe allergic reactions to vaccines are rare but can happen.
  • There is a rare risk of myocarditis and pericarditis associated with mRNA COVID-19 vaccination, mostly among males ages 12–39 years. The rare risk may be further reduced with a longer interval between the first and second dose.
  • Cases of myocarditis and pericarditis have also been reported in people who received Novavax COVID-19 vaccine.
  • There was a potential cause-and-effect relationship between the J&J/Janssen COVID-19 vaccine and a rare and serious adverse event. It was blood clots with low platelets (thrombosis with thrombocytopenia syndrome, or TTS). TTS occured at a rate of about 4 cases per million J&J/Janssen doses and resulted in a small number of deaths. The J&J/Janssen COVID-19 vaccine is no longer available in the U.S.

Learn more about vaccine safety monitoring after a vaccine is authorized or approved for use.

If You Are Allergic to an Ingredient in a COVID-19 Vaccine or Had a Previous Severe Allergic Reaction

  • If in the past you have had a severe allergic reaction to an ingredient in an COVID-19 vaccine or if you have a known allergy to an ingredient in a COVID-19 vaccine, you should not get that COVID-19 vaccine. Examples:
    • If you are allergic to polyethylene glycol (PEG), you should not get Pfizer-BioNTech or Moderna COVID-19 vaccines.
    • If you are allergic to polysorbate, you should not get Novavax COVID-19 vaccines.
  • If you aren’t able to get one type of COVID-19 vaccine, talk to your doctor about your options for getting a different type of COVID-19 vaccine.
Learn About Getting Your Vaccine
  • Do you need to wait to get vaccinated after getting COVID-19 or getting treatment for COVID-19?
  • How can you prepare for vaccination?
  • What can you expect during and after your vaccination?
Getting Your COVID-19 Vaccine