Coronavirus disease 2019 (COVID-19) vaccines provide protection against COVID-19. COVID-19 COVID-19 COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more is the disease caused by infection with the SARS-CoV-2 virus. There are multiple COVID-19 vaccines currently in use worldwide (see COVID-19 Vaccine Tracker). This topic includes only those vaccines currently in use in the United States.
There are two mRNA vaccines approved for use in the United States for COVID-19:
BNT162b2 COVID-19 vaccine (mRNA) (made by Pfizer-BioNTech)
mRNA-1273 COVID-19 vaccine (mRNA) (made by Moderna)
There is one adjuvanted vaccine available for use in the United States for COVID-19:
NVX-CoV2373 COVID-19 vaccine (subunit) (made by Novavax)
There is one adenovirus vector vaccine available for use in the United States for COVID-19:
Ad26.COV2.S COVID-19 vaccine (adenovirus vector) (made by Janssen/Johnson & Johnson)
The BNT162b2 vaccine is approved for use in people 16 years of age and older by the U.S. Food and Drug Administration (FDA). This vaccine also has Emergency Use Authorization (EUA) from the FDA for children 6 months to 15 years of age.
The mRNA-1273 vaccine is approved for use in people 18 years of age and older. This vaccine also has EUA for children 6 months to 17 years of age.
The Ad26.COV2.S vaccine has EUA for people 18 years of age and older who do not have access to or cannot receive other COVID-19 vaccines, or who opt to receive Ad26.COV2.S because they would otherwise not receive any COVID-19 vaccine. (See FDA Limits Use of Janssen COVID-19 Vaccine to Certain Individuals.)
The NVX-CoV2373 vaccine has EUA for people 12 years of age and older.
Vaccination remains the most effective strategy at preventing severe illness and death resulting from COVID-19 infection. Hospitalization rates in the United States in the fall of 2021 were 8 to 10 times higher in unvaccinated people than vaccinated people. Unvaccinated people were also 20 times more likely to die of COVID-19 than vaccinated people in that time frame.
In most situations, the mRNA vaccines and the adjuvanted vaccine are preferred over the adenovirus vector vaccine for primary series doses because some research shows a relationship between the adenovirus vector vaccine and a rare and serious side effect called vaccine-induced thrombotic thrombocytopenia Side Effects Coronavirus disease 2019 (COVID-19) vaccines provide protection against COVID-19. COVID-19 is the disease caused by infection with the SARS-CoV-2 virus. There are multiple COVID-19 vaccines... read more . (See Johnson & Johnson’s Janssen COVID-19 Vaccine Overview and Safety.)
For more information, see the fact sheets for the vaccine providers Pfizer-BioNTech, Moderna, Janssen/Johnson & Johnson, and Novavax.
(See also Overview of Immunization Overview of Immunization Immunization (vaccination) helps the body defend itself against diseases caused by certain bacteria or viruses. Immunity (the ability of the body to defend itself against diseases caused by... read more .)
Administration of COVID-19 Vaccine
The BNT162b2 COVID-19 vaccine (mRNA) made by Pfizer-BioNTech is given as a primary series of 2 injections given at least 3 to 8 weeks apart in people 5 years of age and older.
The BNT162b2 vaccine is given as a primary series of 3 injections in children 6 months to 4 years of age. The second injection is given at least 3 to 8 weeks after the first one. The third injection is the bivalent BNT162b2 vaccine and is given at least 8 weeks after the second one.
The mRNA-1273 COVID-19 vaccine (mRNA) made by Moderna is given as a primary series of 2 injections given at least 4 to 8 weeks apart in people 6 months of age and older.
The Ad26.COV2.S COVID-19 vaccine (adenovirus vector) made by Janssen/Johnson & Johnson is given as 1 primary injection in people 18 years of age and older who do not have access to or cannot receive other COVID-19 vaccines, or who opt to receive Ad26.COV2.S because they would otherwise not receive any COVID-19 vaccine.
NVX-CoV2373 COVID-19 vaccine (subunit) made by Novavax is given as a primary series of 2 injections given at least 3 to 8 weeks apart in people 12 years of age and older.
Additional primary series and booster dose guidance depends on a person's age and on whether they have a weakened or impaired immune system (immunocompromise).
Primary series guidance for people who are moderately to severely immunocompromised
An additional primary series vaccine dose is advised for people with a moderately to severely weakened or impaired immune system. People should talk to their health care practitioner about their medical condition and about whether getting an additional primary series dose is appropriate for them. (See Guidance for COVID-19 vaccination for people who are moderately or severely immunocompromised.)
After a primary series is completed, protection against infection has been shown to decrease over time. To maximize protection against infection, severe disease, and death, booster doses are recommended for people 6 months of age and older. Only a bivalent booster vaccine authorized for that age group should be used. The booster dose should be given 2 months after the primary series is completed. People who have received all recommended primary series vaccinations and booster doses when eligible are considered up-to-date on their vaccine series.
Booster with updated bivalent vaccines
In 2022, the FDA amended the EUA for the mRNA vaccines to authorize bivalent formulations of the vaccines for use as a single booster dose (see the FDA fact sheet). “Bivalent” means the vaccines protect against two components of the SARS-CoV-2 virus. One component is the original strain of SARS-CoV-2, and the other one targets the most recent Omicron subvariants known as BA.4 and BA.5. Since the introduction of the bivalent vaccines, the CDC authorizes use of only the updated bivalent vaccine as a booster. The original booster is monovalent, which means it protects against only one component of the SARS-CoV-2 virus. The monovalent mRNA booster is no longer available.
COVID-19 booster shot guidance for people who are not immunocompromised
People who are not immunocompromised and who are fully vaccinated against COVID-19 are eligible for a booster shot depending on their age and on the primary series they completed (see COVID-19 Vaccine Booster Shots).
COVID-19 booster shot guidance for people who are moderately to severely immunocompromised
People who are moderately to severely immunocompromised and who are fully vaccinated against COVID-19 are eligible for a booster shot depending on their age and on the primary series they completed (see COVID-19 Vaccines for People Who Are Moderately or Severely Immunocompromised).
Side Effects of COVID-19 Vaccine
The four COVID-19 vaccines have similar side effects:
Pain, swelling, and redness at the injection site
Tiredness
Headache
Muscle and joint pains
Fever and chills
Nausea
Swollen lymph nodes
Side effects typically last several days.
There is a very small chance of a severe allergic reaction. This usually occurs within a few minutes to 1 hour after getting a dose of the vaccine and may require emergency treatment. If a person develops difficulty breathing, they or someone with them should call for emergency medical care (911 in the United States) or go to the nearest hospital. People who have had severe allergic reactions to other vaccines or injectable medications should discuss the risk of an allergic reaction with their doctor and be observed after receiving the vaccine.
Very rarely, people develop an unusual problem with excessive blood clotting (thrombosis) and low platelet levels (thrombocytopenia Overview of Thrombocytopenia Thrombocytopenia is a low number of platelets (thrombocytes) in the blood, which increases the risk of bleeding. Thrombocytopenia occurs when the bone marrow makes too few platelets or when... read more 
) after receiving the vaccine made by Janssen/Johnson & Johnson. In this condition, called vaccine-induced thrombosis with thrombocytopenia syndrome, blood clots develop in unusual and critical places, such as in blood vessels in the brain or abdomen. Symptoms begin about 1 to 2 weeks after vaccination. This problem has occurred in men and women 18 years of age and older but is more likely to occur in women 30 to 49 years of age. Some people die. (See also Johnson & Johnson’s Janssen COVID-19 Vaccine Overview and Safety.)
The heart problems myocarditis Myocarditis Myocarditis is inflammation of the muscle tissue of the heart (myocardium) that causes tissue death. Myocarditis may be caused by many disorders, including infection, toxins and drugs that affect... read more and pericarditis Acute Pericarditis Acute pericarditis is inflammation of the pericardium (the flexible two-layered sac that envelops the heart) that begins suddenly, is often painful, and causes fluid and blood components such... read more 
have been reported after doses of the vaccines made by Pfizer-BioNTech, Moderna, and Novavax, particularly within 7 days of the second dose, suggesting there may be an increased risk of these problems after vaccination. The risk is highest in young males. Vaccine recipients should seek medical attention right away if they have chest pain, shortness of breath, or feelings of having a fast-beating, fluttering, or pounding heart after vaccination.
The Centers for Disease Control and Prevention (CDC) states women who are due for a mammogram and who have recently received COVID-19 vaccination ask their doctor how long they should wait after vaccination to get their mammogram because temporary reactions to the vaccine might cause a false reading on the mammogram. Some experts recommend getting the mammogram before the vaccine or waiting 4 to 6 weeks after getting the vaccine.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
U.S. Food and Drug Administration (FDA): Fact sheets for Pfizer-BioNTech
Centers for Disease Control and Prevention (CDC): Vaccines for COVID-19
CDC: COVID-19 vaccination and other medical procedures: Mammograms: Guidance regarding routine mammography before or after COVID-19 vaccination
