Developed by American pharmaceutical company Pfizer and German firm BioNTech, this COVID-19 vaccine was authorized for emergency use by the U. S. Food and Drug Administration on December 11, 2020. The Pfizer vaccine was the first COVID-19 vaccine made available in the United States.

Important Information about the Pfizer Vaccine

  • Number of doses required: 2 doses of the same vaccine
  • Time between doses: Minimum of 21 days
  • Authorized for: People age 16 and up
  • How long before full protection begins: 2 weeks after second dose
  • Effectiveness: 95 percent
  • How long protection will last: Unknown at this time; study is ongoing
  • Storage: Ultracold temperature as low as -112 degrees Fahrenheit

Testing of the vaccine in children or pregnant or breastfeeding women has not been completed, so there are not sufficient data on the vaccine in those groups. However, more studies in both these groups with be forthcoming.

While children under the age of 16 are not eligible to receive the vaccine at this time, pregnant and breastfeeding women can receive it. They should talk to their healthcare provider about the vaccine.

How the Pfizer Vaccine Works

Both the Pfizer and Moderna COVID-19 vaccines are based on messenger RNA (mRNA) technology. mRNA vaccines contain a code that provides the cells "instructions" to create antibodies to protect against COVID-19. Learn more about how mRNA vaccines work.

This type of vaccine does not contain any part of the virus, so it cannot cause COVID-19.

How the Vaccines Were Developed

Although the vaccines were developed in less than a year, they went through the same rigorous approval process. Learn more about the vaccines' development and approval process.

In May, the University of Maryland School of Medicine (UMSOM) became the first in the United States to begin testing this COVID-19 vaccine candidate. Learn more about how we're fighting COVID at the University of Maryland Medical System.

Special Considerations

Side Effects of the Pfizer Vaccine

Possible side effects, which usually go away within 24-48 hours after receiving the vaccine, include:

  • Pain, swelling and/or redness at the injection site
  • Fatigue and/or feeling unwell
  • Headache
  • Joint and muscle pain
  • Chills and/or fever
  • Nausea
  • Swollen lymph nodes

Possible Allergic Reactions to the Pfizer Vaccine

While severe allergic reactions have been extremely rare, there is a slight risk of an allergic reaction to the Pfizer vaccine. Signs of an allergic reaction may include:

  • Difficulty breathing
  • Swelling of your face and throat
  • A fast heartbeat
  • A bad rash all over your body
  • Dizziness and weakness

If you have a history of severe allergic reactions, talk to your doctor before receiving the vaccine and tell your vaccine provider about your history of allergies. You will also be monitored for 30 minutes after your vaccination.

If you have a severe allergic reaction to the first dose of this vaccine, you should not receive the second dose. If you are allergic to any ingredient of the vaccine, you should not receive the vaccine. Please see the FDA fact sheet for information on vaccine ingredients for Pfizer.

The vaccine does not contain any egg-based technology, so there is no concern for people with egg allergies like there may be with other vaccines.

Other Conditions

Before you get vaccinated, you should talk to your doctor if you:

  • Have any allergies
  • Have a fever
  • Have a bleeding disorder or are on a blood thinner
  • Are immunocompromised or are taking a medicine that affects your immune system
  • Are pregnant or plan to become pregnant
  • Are breastfeeding
  • Have received another COVID-19 vaccine

Updated 1/7/2021

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