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COVID-19 Vaccine

By

Margot L. Savoy

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

Last review/revision Oct 2022
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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, 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 resulting from SARS-CoV-2 infection with the recent and currently circulating variants, Delta and Omicron. Hospitalization rates in the US 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 during that time frame.

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 US.

In the US, 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) adenovirus vector vaccine produced by Janssen/Johnson & Johnson has EUA for people 18 years of age and older for whom other COVID-19 vaccines are not accessible or clinically appropriate, or who elect 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.)

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

In most situations, the mRNA vaccines and the Novavax spike protein vaccine are preferred over the adenovirus vector vaccine for primary series doses because of the risk of serious adverse events. There is a plausible causal relationship between the adenovirus vector vaccine and the rare and serious adverse event vaccine-induced thrombosis with thrombocytopenia syndrome Contraindications and Precautions 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 . (See Johnson & Johnson’s Janssen COVID-19 Vaccine Overview and Safety.)

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 and the FDA prescribing information for the Moderna COVID-19 vaccine, and the EUA fact sheets for vaccination providers (Pfizer-BioNTech, Moderna, Janssen/Johnson & Johnson, and Novavax). A summary of changes to the 2022 adult immunization schedule is available here.

Preparations

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 adenovirus vector vaccine for COVID-19:

  • Ad26.COV2.S (produced by Janssen/Johnson & Johnson)

The adenovirus vector vaccine contains a piece of the DNA that is used to make the distinctive spike protein of the SARS-CoV-2 virus, which then triggers the desired immune response.

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

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

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

The mRNA-1273 vaccine has FDA approval for the prevention of COVID-19 in people 18 years of age and older.

The mRNA-1273 vaccine has EUA for the prevention of COVID-19 in people 6 months to 17 years of age.

The Ad26.COV2.S vaccine has EUA for the prevention of COVID-19 in people 18 years of age and older for whom other COVID-19 vaccines are not accessible or clinically appropriate, or who elect 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 the prevention of COVID-19 in people 12 years of age and older.

Contraindications and Precautions

Contraindications for all four COVID-19 vaccines are

  • Severe allergic reaction after a previous dose of either vaccine

  • Severe allergic reaction to a vaccine component

Precautions for all four 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 adenovirus vector vaccine because cases of vaccine-induced thrombosis with thrombocytopenia syndrome have been reported after vaccination (see FDA fact sheet for Janssen/Johnson & Johnson). Reports suggest an increased risk of thrombosis involving the cerebral venous sinuses and other sites (including but not limited to the central and visceral arteries and the veins and arteries of the lower extremities) combined with thrombocytopenia. Symptom onset is about 1 to 2 weeks after vaccination. Cases have occurred in males and females 18 years of age and older, and females 30 to 49 years of age have the highest reporting rate; some have been fatal. The use of heparin may be harmful in people with suspected thrombosis with thrombocytopenia after vaccination; alternative treatments may be needed. Consultation with hematology specialists is strongly recommended. (See also Johnson & Johnson’s Janssen COVID-19 Vaccine Overview and Safety.)

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

BNT162b2 COVID-19 vaccine (mRNA) primary series dosage information for children and adults is available here.

mRNA-1273 COVID-19 vaccine (mRNA) primary series dosage information for children and adults is available here.

Ad26.COV2.S COVID-19 vaccine (adenovirus vector) primary series dosage information for adults is available here.

NVX-CoV2373 COVID-19 vaccine (spike protein) primary series dosage information for children and adults is available here.

Additional primary series and booster dose guidance depends on a person's age and immunocompromise status.

Primary series guidance for people who are moderately to severely immunocompromised

An additional primary series dose is advised for people with a moderately to severely compromised immune system (see Guidance for COVID-19 vaccination for people who are moderately or severely immunocompromised and see COVID-19 Vaccines 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. Only a bivalent booster vaccine authorized for that age group should be used. 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). 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.

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).

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).

Adverse Effects

The four COVID-19 vaccines have similar adverse effects.

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. The Centers for Disease Control and Prevention (CDC) states that some experts recommend getting the mammogram before the vaccine or waiting 4 to 6 weeks after getting the vaccine.

More Information

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
Janssen COVID-19 Vaccine
Novavax COVID-19
Hepflush-10 , Hep-Lock, Hep-Lock U/P, Monoject Prefill Advanced Heparin Lock Flush, SASH Normal Saline and Heparin
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NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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