Vaccine

Updated June 14, 2021

Update: The Centers for Disease Control and Prevention (CDC) is monitoring reports of the heart conditions myocarditis and pericarditis in people who received the Moderna and Pfizer-BioNTech vaccines, especially adolescents and young adults.

According to the CDC, the reported cases were rare and happened mostly in male adolescents and young adults 16 and older. Symptoms usually presented within days of vaccination, and patients typically responded well to rest and medications.

The CDC continues to recommend vaccination for Americans 12 and older.

In December, the Food and Drug Administration (FDA) granted Emergency Use Authorization (EUA) for two COVID-19 vaccines. An EUA means the FDA has determined the vaccines are safe and effective enough to recommend for preventing COVID-19. No COVID-19 vaccine has received full FDA approval as past vaccines have, which takes more time.

The pharmaceutical companies Pfizer and BioNTech developed one, and the company Moderna developed the other. While both vaccines are mRNA vaccines that require two doses, they have some differences as well.

On May 10, 2021, the FDA authorized the Pfizer vaccine for adolescents age 12-15. Americans 12 and older are eligible for the Pfizer vaccine. The Moderna vaccine is currently available for Americans 18 and older.

Below is more on how the Moderna and Pfizer vaccines work, how they are similar, and how they differ.

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How mRNA Vaccines Work

Both vaccines are messenger RNA (mRNA) vaccines that contain genetic instructions, called mRNA, for making the spike protein. This protein is a molecule found on the outside of the coronavirus that causes COVID-19. One way your body’s immune system recognizes the coronavirus as an intruder is by this spike protein.

Once the vaccine is in the body, cells pick up the mRNA and follow the instructions to make spike proteins. Then the cell displays the spike protein on its outer surface similar to the way a coronavirus does. Because these spike proteins are still only a piece of the whole coronavirus, they cannot harm the body on their own.

When the immune system sees the spike protein, it recognizes it as an intruder and begins building antibodies against it. Antibodies are customized proteins that help the immune system attack any virus carrying that spike protein.

The immune system then stores these antibodies, which can fight the real virus too. The immune system also remembers how to make more of these antibodies if necessary.

The vaccine does not affect your cells’ DNA in any way, and the immune system does not attack your own cells. It will only attack a coronavirus that enters the body and has that spike protein.

Similar Vaccine Effectiveness

Both vaccines have high effectiveness based on clinical trials in tens of thousands of people of different races and ethnicities. The Pfizer vaccine protects 95% of people who receive it from COVID-19 disease. The Moderna vaccines protects 94% of people who receive it from COVID-19 disease.

Both vaccines also protect against severe disease in the small number of people who still develop COVID-19 after vaccination. None of the people who received either vaccine during clinical trials needed hospitalization.

Neither vaccine has been tested in children or people who are pregnant, breastfeeding, taking anti-clotting medications, or taking immune-suppressing medication.

Similar Side Effects and Vaccine Safety

The Pfizer and Moderna vaccines have similar side effects. Many people who receive either vaccine had mild pain at the injection site, tiredness, or headache. The following mild side effects were also common in both vaccines:

  • Muscle pain
  • Fever
  • Chills
  • Joint pain
  • Nausea or vomiting

A severe allergic reaction, called anaphylactic reactions, are possible with any vaccine, including both the Pfizer and Moderna vaccines. A severe anaphylactic reaction means the person has to use an EpiPen or other epinephrine device or to go to the hospital.

Anaphylaxis is rare, according to monitoring data and clinical trials. People who have a history of allergy or anaphylaxis should follow guidelines on receiving or deferring the vaccine. Everyone should monitor their symptoms and seek care if they experience a reaction.

Everyone who had severe allergic reactions received treatment and recovered completely. No one has died because of receiving the Pfizer or Moderna vaccines. People with a history of severe anaphylactic reactions should speak to their doctor with any questions about getting the vaccine.

The CDC is monitoring reports of the heart conditions myocarditis and pericarditis in people who received the Moderna and Pfizer vaccines, especially adolescents and young adults.

According to the CDC, the reported cases were rare and happened mostly in male adolescents and young adults 16 and older. Symptoms usually presented within days of vaccination, and patients typically responded well to rest and medications.

The CDC continues to recommend vaccination for Americans 12 and older.

Differences Between Pfizer and Moderna Vaccines

The Pfizer vaccine can be administered to anyone age 12 and older while only adults age 18 and older can receive the Moderna vaccine. Both companies are currently testing the vaccine in adolescents and younger children.

Both vaccines require two doses, but the time between doses is different. People receive the second dose of the Pfizer vaccine is at least 21 days after the first dose. The time between Moderna doses is at least 28 days.

Both vaccines require specialized cold storage, but the Pfizer vaccine has much colder temperature requirements. The Pfizer vaccine requires -94º F (-75º C) for shipping and storage, much colder than typical freezers at doctors’ offices and pharmacies. After it thaws, the Pfizer vaccine remains good for 5 days in a normal refrigerator.

The Moderna vaccine requires -4º F (-20º C) for shipping and storage, similar to a typical home freezer. Once opened, the Moderna vaccine remains good at refrigerator temperature for 30 days and at room temperature for 12 hours.

Sources

Dr. Aaron E. Carroll. The Risks of the Covid Vaccine, in Context. Dec. 30, 2020. New York Times. Link

Fact Sheet for Healthcare Providers Administering Vaccine (Vaccination Providers). Emergency Use Authorization (EUA) of the Moderna COVID-19 Vaccine to Prevent Coronavirus Disease 2019. US Food and Drug Administration. Link

Fact Sheet for Healthcare Providers Administering Vaccine (Vaccination Providers). Emergency Use Authorization (EUA) of the Pfizer-BioNTech COVID-19 Vaccine to Prevent Coronavirus Disease 2019. US Food and Drug Administration. Link

Fact Sheet for Recipients and Caregivers. Emergency Use Authorization (EUA) of the Moderna COVID-19 Vaccine to Prevent Coronavirus Disease 2019. US Food and Drug Administration. Link

Fact Sheet for Recipients and Caregivers. Emergency Use Authorization (EUA) of the Pfizer-BioNTech COVID-19 Vaccine to Prevent Coronavirus Disease 2019. US Food and Drug Administration. Link

MRNA-1273. Sponsor Briefing Document. Vaccines and Related Biological Products Advisory Committee. Briefing Document. December 17, 2020. US Food and Drug Administration. Link

National Center for Immunization and Respiratory Diseases (NCIRD), Division of Viral Diseases. COVID-19 Vaccines and Severe Allergic Reactions. Centers for Disease Control and Prevention. Link

National Center for Immunization and Respiratory Diseases (NCIRD), Division of Viral Diseases. Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines Currently Authorized in the United States. Centers for Disease Control and Prevention. Link

National Center for Immunization and Respiratory Diseases (NCIRD), Division of Viral Diseases. Information about the Moderna COVID-19 Vaccine. Centers for Disease Control and Prevention. Link

National Center for Immunization and Respiratory Diseases (NCIRD), Division of Viral Diseases. Information about the Pfizer-BioNTech COVID-19 Vaccine. Centers for Disease Control and Prevention. Link

National Center for Immunization and Respiratory Diseases (NCIRD), Division of Viral Diseases. Understanding mRNA COVID-19 Vaccines. Centers for Disease Control and Prevention. Link

Noah Weiland, Denise Grady and Carl Zimmer. Moderna Vaccine Is Highly Protective Against Covid-19, the F.D.A. Finds. December 18, 2020. The New York Times. Link

Pfizer-BioNTech COVID-19 Vaccine (BNT162, PF-07302048). Vaccines and Related Biological Products Advisory Committee. Briefing Document. December 10, 2020. US Food and Drug Administration. Link

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