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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 Dec 2021
CLICK HERE FOR THE PROFESSONAL VERSION

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 a newly identified coronavirus officially named SARS-CoV-2. COVID-19 was first reported in late 2019 in Wuhan, China... read more is the disease caused by infection with the SARS-CoV-2 virus. There are multiple COVID-19 vaccines currently in use worldwide. This topic includes only those vaccines currently in use in the United States.

In the United States, the Pfizer COVID-19 vaccine (mRNA) has been approved for use in people 16 years of age and older by the U.S. Food and Drug Administration (FDA). The Pfizer vaccine also received Emergency Use Authorization (EUA) from the FDA for children 5 to 15 years of age. Two other vaccines, Moderna COVID-19 vaccine (mRNA) and Johnson & Johnson COVID-19 vaccine (adenovirus vector), received EUA for people 18 years of age and older.

For more information, see the FDA news release for the Pfizer-BioNTech vaccine approval and see the EUA fact sheets for the Pfizer, Moderna, and Johnson & Johnson vaccines.

All 3 vaccines completely prevented serious complications of COVID-19 including hospitalizations and deaths in clinical trials. In a clinical trial, the Pfizer vaccine prevented COVID-19 disease in 95% of people following 2 doses given 3 weeks apart. In a separate trial, the Moderna vaccine prevented COVID-19 disease in 94.1% of people. The Johnson & Johnson vaccine prevented COVID-19 disease in about 67% of people overall and prevented severe/critical COVID-19 disease in 85% after one dose. It is important to note that these trials cannot be compared directly because they were done on different groups of people at different points in the pandemic. The duration of the protection from the vaccines is currently not known. People with a weakened immune system, including those taking immunosuppressant drugs, may have a diminished response to the vaccine. Although these vaccines decrease the likelihood and severity of infection, it is not currently known how well vaccines prevent the spread of the virus that causes COVID-19. Thus, people who have been vaccinated should still follow the same general prevention measures recommended for unvaccinated people in the same region, including mask wearing, social distancing, and frequent hand washing.

Administration of COVID-19 Vaccine

The Pfizer-BioNTech COVID-19 vaccine (mRNA) has FDA approval for use in people 16 years of age and older and is given as a series of 2 injections given 3 weeks apart.

The Pfizer-BioNTech COVID-19 vaccine (mRNA) received EUA for use in people 5 to 15 years of age and is given as a series of 2 injections given 3 weeks apart.

The Moderna COVID-19 vaccine (mRNA) received EUA for use in people 18 years of age and older and also requires 2 injections but given 4 weeks apart.

The Johnson & Johnson COVID-19 vaccine (adenovirus vector) received EUA for use in people 18 years of age and older and requires only a single injection.

An additional primary series dose of the Pfizer or Moderna vaccine received EUA and is recommended for people with a moderately to severely weakened or impaired immune system. This additional dose should be given after an initial 2-dose series is completed. 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 COVID-19 Vaccines for Moderately to Severely Immunocompromised People.) The additional primary series dose applies to the following people:

  • Moderately to severely immunocompromised people 18 years of age and older who completed their Moderna vaccine primary series should plan to get an additional primary dose 28 days after receiving their second shot.

  • Moderately to severely immunocompromised people 12 years of age and older who completed their Pfizer vaccine primary series should plan to get an additional primary dose 28 days after receiving their second shot.

  • Moderately to severely immunocompromised people 18 years of age and older who received a Pfizer or Moderna primary series and an additional primary dose are eligible to receive a booster shot COVID-19 booster shots read more .

Moderately to severely immunocompromised people 18 years of age and older who received the Johnson & Johnson vaccine should not receive an additional primary dose. However, they should get a booster shot COVID-19 booster shots read more .

COVID-19 booster shots

People age 18 years and older who are fully vaccinated against COVID-19 are eligible for a booster shot (see COVID-19 Vaccine Booster Shots):

  • Booster doses are recommended for all Pfizer and Moderna vaccine recipients age 18 years and older and who completed their initial 2-dose series (or their third primary dose, if immunocompromised) 6 or more months ago.

  • Booster doses are recommended for Johnson & Johnson vaccine recipients who are age 18 years and older and who received their first dose 2 or more months ago.

  • Eligible people may choose to receive a booster dose of any available COVID-19 vaccine (Pfizer, Moderna, or Johnson & Johnson), regardless of which vaccine they initially received.

People 16 and 17 years of age who completed their initial 2-dose series (or their third primary dose, if immunocompromised) of the Pfizer vaccine 6 or more months ago are eligible for a booster dose of the Pfizer vaccine only. Unlike people 18 years of age and older who can choose any available COVID-19 vaccine as a booster shot, only a Pfizer booster shot is available to eligible people 16 and 17 years of age.

People 16 and 17 years of age who received the Moderna or Johnson & Johnson primary dose series are not eligible for a booster shot. (See COVID-19 Vaccine Booster Shots.)

Side Effects of COVID-19 Vaccine

The three 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

  • Feeling unwell

  • Swollen lymph nodes

Side effects typically last several days. For the Pfizer-BioNTech and Moderna COVID-19 vaccines, more people have side effects after the second dose than after the first dose.

There is a remote chance of a severe allergic reaction. This usually occurs within a few minutes to 1 hour after getting a dose of the vaccine and requires emergency treatment (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 drugs should discuss the risk of an allergic reaction with their doctor and be observed after receiving the vaccine. Signs of a severe allergic reaction include

  • Difficulty breathing

  • Swelling of face and throat

  • A fast heartbeat

  • A bad rash all over body

  • Dizziness and weakness

People should not get the Pfizer-BioNTech or Moderna vaccine if they have had a severe allergic reaction to a previous dose of the vaccine or to any component of the vaccine (including polyethylene glycol [PEG]). People should not get the Janssen vaccine if they have a history of severe allergic reaction to any of its ingredients.

Very rarely, people (mostly women) 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 Overview of Thrombocytopenia ) after vaccination. In this condition, called vaccine-induced thrombotic thrombocytopenia, blood clots develop in unusual and critical places, such as in blood vessels in the brain or abdomen.

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 Acute Pericarditis have been reported following the second dose of the Pfizer and Moderna vaccines, suggesting there may be an increased risk of these problems after vaccination. The risk is highest in men 18 to 24 years of age. 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.

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