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COVID-19 Vaccine

By

Margot L. Savoy

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

Last full review/revision Jun 2021| Content last modified May 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. COVID-19 was first reported in late 2019 in Wuhan, China and has since spread extensively... read more . COVID-19 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 US.

In the US, the COVID-19 vaccine (mRNA) produced by Pfizer-BioNTech (brand name Comirnaty) 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 5 to 15 years of age. COVID-19 vaccine (mRNA) produced by Moderna (brand name Spikevax) is approved for use in people 18 years of age and older. COVID-19 vaccine (adenovirus vector) 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.)

Vaccination remains the most effective strategy in preventing severe illness and death resulting from COVID-19 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. Data from South Africa indicate that 2 doses of the vaccine produced by Pfizer-BioNTech is 70% effective against the Omicron variant ( 1 Vaccination references COVID-19 is an acute, sometimes severe, respiratory illness caused by the novel coronavirus SARS-CoV-2. COVID-19 was first reported in late 2019 in Wuhan, China and has since spread extensively... read more ). (For more on vaccine efficacy, see COVID-19 prevention COVID-19 vaccination .)

In most situations, the mRNA vaccines are preferred over the adenovirus vector vaccine for primary series and booster 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. COVID-19 is the disease caused by infection with the SARS-CoV-2 virus. There are multiple COVID-19 vaccines currently in use worldwide... 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 news release for Pfizer-BioNTech COVID-19 vaccine approval and the FDA news release for Moderna COVID-19 vaccine approval, and the EUA fact sheets for vaccination providers (Pfizer-BioNTech, Moderna, and Janssen/Johnson & Johnson). A summary of changes to the 2021 adult immunization schedule is available here.

General reference

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.

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 5 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 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.)

Contraindications and Precautions

Contraindications for the mRNA vaccines are

  • Severe allergic reaction after a previous dose of either vaccine

  • Severe allergic reaction to a vaccine component

The main contraindication for the adenovirus vector vaccine is

  • Severe allergic reaction to a vaccine component

Precautions for all three 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 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 the second 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 and the vaccine produced by Moderna). 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

The BNT162b2 COVID-19 vaccine (mRNA) dose is 0.3 mL (30 mcg) IM, given in a 2-dose primary series 3 weeks apart, for people 12 years of age and older.

The BNT162b2 vaccine dose is 0.2 mL (10 mcg) IM, given in a 2-dose primary series 3 weeks apart, for people 5 to 11 years of age.

The mRNA-1273 COVID-19 vaccine (mRNA) dose is 0.5 mL IM, given in a 2-dose primary series 4 weeks apart, for people 18 years of age and older.

The Ad26.COV2.S COVID-19 vaccine (adenovirus vector) dose is 0.5 mL IM, given in 1 injection, for people 18 years of age and older.

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 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):

  • Moderately to severely immunocompromised people 18 years of age and older who completed the primary series of the mRNA-1273 vaccine (produced by Moderna) should get an additional primary dose at least 28 days after receiving their second dose.

  • Moderately to severely immunocompromised people 5 years of age and older who completed the primary series of the BNT162b2 vaccine (produced by Pfizer-BioNTech) should get an additional primary dose at least 28 days after receiving their second dose.

  • Moderately to severely immunocompromised people 18 years of age and older who received the Ad26.COV2.S vaccine (produced by Janssen/Johnson & Johnson) should get a second shot (additional dose) using an mRNA COVID-19 vaccine at least 28 days after receiving their Ad26.COV2.S dose.

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 2 to 5 months after the primary series is completed. Studies have shown vaccine boosting reduces severe disease 20-fold and decreases mortality by 90% compared to primary series alone. People who have received a booster dose when eligible are considered up-to-date on their vaccine series.

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):

  • A first booster dose of BNT162b2 vaccine is recommended for all BNT162b2 vaccine recipients age 5 years and older and who completed their primary series 5 or more months ago.

  • A first booster dose of mRNA-1273 vaccine is recommended for all mRNA-1273 vaccine recipients age 18 years and older and who completed their primary series 5 or more months ago.

  • A first booster dose of BNT162b2 vaccine or mRNA-1273 vaccine is recommended for Ad26.COV2.S vaccine recipients who are age 18 years and older and who received their dose 2 or more months ago.

  • A second booster dose of BNT162b2 vaccine or mRNA-1273 vaccine may be given to people 50 years of age and older at least 4 months after receiving a first booster dose of any available COVID-19 vaccine (BNT162b2, mRNA-1273, or Ad26.COV2.S).

Eligible people 18 years of age and older may choose to receive a booster dose of any available COVID-19 vaccine, regardless of which vaccine they initially received, but the mRNA vaccines are preferred in most cases because of the risk of vaccine-induced thrombosis with thrombocytopenia syndrome with the vector vaccine. Only BNT162b2 is currently approved for children 5 to 17 years of age.

Booster shot guidance for people who are moderately to severely immunocompromised

  • Moderately to severely immunocompromised people 18 years of age and older who completed the primary series of the BNT162b2 vaccine (produced by Pfizer-BioNTech) or the mRNA-1273 vaccine (produced by Moderna) should get a booster shot of the BNT162b2 or mRNA-1273 vaccine at least 3 months after the third primary dose. A second booster dose may be given at least 4 months after the first booster dose.

  • Moderately to severely immunocompromised people 12 to 17 years of age who completed the primary series of the BNT162b2 vaccine should get a booster shot at least 3 months after the third primary dose. A second booster dose may be given at least 4 months after the first booster dose.

  • Moderately to severely immunocompromised people 5 to 11 years of age who completed the primary series of the BNT162b2 vaccine should get a booster shot of the BNT162b2 vaccine at least 3 months after the third primary dose.

  • Moderately to severely immunocompromised people 18 years of age and older who received the Ad26.COV2.S vaccine (produced by Janssen/Johnson & Johnson) should get a booster shot at least 2 months after the additional primary mRNA COVID-19 vaccine dose. (People who received a primary dose of the Ad26.COV2.S vaccine and already received a first booster dose without having had the mRNA primary dose should get an mRNA vaccine as a third dose at least 2 months after the booster dose.) A second booster dose (fourth shot) with an mRNA COVID-19 vaccine may be given at least 4 months after the prior dose.

Adverse Effects

The three 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. For vaccines requiring a 2-dose primary series, more people have adverse effects after the second dose than after the first dose.

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

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

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NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
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