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COVID-19 Vaccine


Margot L. Savoy

, MD, MPH, Lewis Katz School of Medicine at Temple University

Reviewed/Revised Jul 2023

COVID-19 vaccines provide protection against COVID-19 COVID-19 COVID-19 is an acute, sometimes severe, respiratory illness caused by the novel coronavirus SARS-CoV-2. Prevention is by vaccination and infection control precautions (eg, face masks, handwashing... read more , the disease caused by infection with the SARS-CoV-2 virus. Vaccination is the most effective strategy to prevent severe illness and death from SARS-CoV-2 infection. From January 2021 to April 2022, when the Omicron variant was predominant, hospitalization rates were 10.5 times higher in unvaccinated people and 2.5 times higher in vaccinated people with no booster dose, respectively, compared with those who had received a booster dose (1 Reference COVID-19 vaccines provide protection against COVID-19, the disease caused by infection with the SARS-CoV-2 virus. Vaccination is the most effective strategy to prevent severe illness and death... read more ).

There are multiple COVID-19 vaccines currently in use worldwide (see the UNICEF COVID-19 Vaccine Market Dashboard and WHO Coronavirus [COVID-19] Dashboard); this topic includes only those vaccines currently in use in the United States.

In the United States, the following COVID-19 vaccines are in use:

  • SARS-CoV-2 virus (COVID-19) mRNA vaccine produced by Pfizer-BioNTech has been approved for use in people 16 years of age and older by the U.S. Food and Drug Administration (FDA). This vaccine also received Emergency Use Authorization (EUA) for children 6 months to 15 years of age.

  • SARS-CoV-2 virus (COVID-19) mRNA vaccine produced by Moderna is approved for use in people 18 years of age and older. This vaccine also received EUA for children 6 months to 17 years of age.

  • SARS-CoV-2 virus (COVID-19) recombinant spike protein nanoparticle vaccine produced by Novavax has EUA for people 12 years of age and older.

The SARS-CoV-2 virus (COVID-19) adenovirus vector vaccine produced by Janssen/Johnson & Johnson is no longer available in the United States (see CDC: Janssen (Johnson & Johnson) COVID-19 Vaccine).

For more information, see the COVID-19 Advisory Committee on Immunization Practices Vaccine Recommendations, the FDA prescribing information for the Pfizer-BioNTech COVID-19 vaccine, the FDA prescribing information for the Moderna COVID-19 vaccine, and the EUA fact sheets (Pfizer-BioNTech, Moderna, and Novavax). For a summary of changes to the 2023 adult immunization schedule, including changes to the COVID-19 vaccine information, see the Advisory Committee on Immunization Practices Recommended Adult Immunization Schedule, United States, 2023: Changes to the 2023 Adult Immunization Schedule.


  • 1. Havers FP, Pham H, Taylor CA, et al: COVID-19-Associated Hospitalizations Among Vaccinated and Unvaccinated Adults 18 Years or Older in 13 US States, January 2021 to April 2022. JAMA Intern Med 182(10):1071-1081, 2022. doi:10.1001/jamainternmed.2022.4299

Preparations of COVID-19 Vaccine

There are two mRNA vaccines for COVID-19:

  • BNT162b2 (produced by Pfizer-BioNTech)

  • mRNA-1273 (produced by Moderna)

The mRNA vaccines do not contain viral antigen but rather deliver a small, synthetic piece of mRNA that encodes for the desired target antigen (the spike protein). After being taken up by cells of the immune system, the vaccine mRNA degrades after instructing the cell to produce viral antigen. The antigen is then released and triggers the desired immune response to prevent severe infection upon subsequent exposure to the actual virus.

There is one spike protein vaccine for COVID-19:

  • NVX-CoV2373 (produced by Novavax)

The spike protein vaccine contains a recombinant form of the SARS-CoV-2 spike protein, which then triggers the desired immune response.

Indications for COVID-19 Vaccine

The BNT162b2 vaccine has FDA approval for the prevention of COVID-19 in people 16 years of age and older and EUA for people 6 months to 15 years of age.

The mRNA-1273 vaccine has FDA approval for people 18 years of age and older and EUA for people 6 months to 17 years of age.

The NVX-CoV2373 vaccine has EUA for people 12 years of age and older.

Contraindications and Precautions for COVID-19 Vaccine

Contraindications for COVID-19 vaccines are

  • Severe allergic reaction after a previous dose of either vaccine

  • Severe allergic reaction to a vaccine component

Precautions for COVID-19 vaccines are

Appropriate medical treatment to manage immediate allergic reactions must be immediately available in the event an acute anaphylactic reaction occurs after any COVID-19 vaccine is given. COVID-19 vaccine recipients should be monitored for immediate adverse reactions.

Immunocompromised people, including those receiving immunosuppressant therapy, may have a diminished immune response to these vaccines.

A warning has been issued from the FDA for the mRNA vaccines and the adjuvanted vaccine that myocarditis Myocarditis Myocarditis is inflammation of the myocardium with necrosis of cardiac myocytes. Myocarditis may be caused by many disorders (eg, infection, cardiotoxins, drugs, and systemic disorders such... read more Myocarditis and pericarditis Pericarditis Pericarditis is inflammation of the pericardium, often with fluid accumulation in the pericardial space. Pericarditis may be caused by many disorders (eg, infection, myocardial infarction, trauma... read more Pericarditis have been reported after doses of these vaccines, particularly within 7 days of the second dose, suggesting there may be an increased risk of these events after vaccination (see FDA information for the vaccine produced by Pfizer-BioNTech, the vaccine produced by Moderna, and the vaccine produced by Novavax). The observed 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. Although some people have required intensive care, data from short-term follow-up studies suggest that symptoms usually resolved with conservative management.

Dose and Administration of COVID-19 Vaccine

For COVID-19 vaccinations available for use in the United States, all dose and administration information, including for primary series and recommended booster doses for all age groups and people with special conditions, is available from the CDC at Interim Clinical Considerations for Use of COVID-19 Vaccines Currently Approved or Authorized in the United States.

COVID-19 vaccine doses should be administered by the intramuscular route.

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). The bivalent vaccines (referred to as updated boosters) contain two mRNA 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 (monovalent) mRNA booster is no longer available.

A booster dose of the recombinant spike protein nanoparticle vaccine produced by Novavax (instead of a bivalent mRNA booster dose) may be used in limited situations in people ages 18 years and older who completed any FDA-approved or FDA-authorized monovalent primary series, have not received any previous booster dose(s), and are unable or unwilling to receive an mRNA vaccine and would otherwise not receive a booster dose.

Adverse Effects of COVID-19 Vaccine

The COVID-19 vaccines all have similar adverse effects. (See CDC: Possible Side Effects After Getting a COVID-19 Vaccine.)

Other adverse effects are common:

  • Injection site pain, swelling, and redness

  • Fatigue

  • Headache

  • Muscle and joint pains

  • Fever and chills

  • Nausea

  • Malaise

  • Lymphadenopathy

Adverse effects typically last several days.

Reactive lymphadenopathy may occur after COVID-19 vaccination and may result in a false-positive reading on mammography. Multiple studies have been done, and the most recent recommendation from the Society of Breast Imaging, released in February 2022, recommends no delay between COVID vaccination and screening mammogram (see Society of Breast Imaging: 2022 Position Statements and Recommendations: Revised SBI Recommendations for the Management of Axillary Adenopathy in Patients with Recent COVID-19 Vaccination).

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

Drugs Mentioned In This Article

Drug Name Select Trade
COMIRNATY COVID-19, Moderna COVID-19, Moderna COVID-19 Bivalent, Pfizer-BioNTech COVID-19, Pfizer-BioNTech COVID-19 Bivalent, spikevax COVID-19 mRNA
Novavax COVID-19
Janssen COVID-19 Vaccine
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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