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Understanding the Pfizer-BioNTech and Moderna COVID-19 Vaccines

Moderna and Pfizer-BioNTech have both developed safe, effective vaccines protecting against severe COVID-19 illness that have received an Emergency Use Authorization (EUA) by the Food and Drug Administration in December. To better understand the differences and similarities between the two vaccines – and what that means for you – please reference the information outlined below.

The two vaccines are virtually identical in most aspects, which include:

  • Technology

    • Both Moderna and Pfizer vaccines are based on mRNA technology, which shows our bodies how to make the spike protein found in the SARS-Cov-2 virus (and that it uses to invade our cells). If ever infected with the actual virus, the immune system is then triggered to produce antibodies toward it to prevent illness.
  • Efficacy

    • Both vaccines are approximately 95% effective in preventing COVID-19 illness after two doses.
    • No other vaccines should be administered within 14 days prior or after receiving either the Moderna or Pfizer COVID-19 vaccine.
  • Safety

    • Both vaccines were found to be extremely tolerable, with no serious safety concerns identified in Phase 3 clinical trials.
  • Side effects

    • Approximately 80% of people may develop a mild local symptom (pain at injection site).
    • Some may develop more systemic symptoms (fatigue, body aches, chills, fever, etc.) that subside after approximately 24 hours.
  • Second dose requirement and interval

    • UW Medicine is scheduling second doses of both the Pfizer and Moderna vaccine at a minimum 24 days after the first dose.
    • There is no upper limit to receiving second dose, but the ideal timing is before 28 days since the first dose.
  • Full vaccination status

    • Patients can be considered fully vaccinated one to two weeks after receiving either vaccine.
  • COVID-19 exposure or illness

    • If you have had COVID-19 in the past 90 days, you may wait to receive the vaccine until the end of the 90-day period.
    • With both vaccines, if you are diagnosed with COVID-19 between doses, you should defer your second dose until your symptoms have completely resolved and your healthcare provider has deemed you are safe to return to work.
  • Bell’s Palsy or Guillain-Barre Syndrome (GBS)

    • No cases of GBS have been reported with either of the two COVID-19 mRNA vaccines. Per CDC guidance, persons with a history of GBS may receive either of the mRNA vaccines. Similarly, there have not been cases of Bell’s Palsy reported higher than baseline rates among unvaccinated individuals.

There are also a few key differences between the two vaccines:

  • Storage

    • Pfizer – must be shipped and maintained at -94 degrees Fahrenheit for long-term storage, but can be placed in a refrigerator for up to five days
    • Moderna – can be shipped and maintained at a standard freezer temperature of -4 degrees Fahrenheit, and can stay in a refrigerator for up to 30 days
  • Dilution

    • Pfizer – vial must be thawed and then diluted with saline prior to injection
    • Moderna – ready to be administered as is
  • Minimum age to vaccinate

    • Pfizer – 16 years of age
    • Moderna – 18 years of age (however the company has begun testing the vaccine in 12- to 17-year olds)

If you have any other questions, please read the UW Medicine COVID-19 Vaccine FAQ, reach out to your manager or contact the UW Medicine vaccine team at uwm-eoc-vaccines@uw.edu. Employees and students may also call the vaccine hotline at 206.520.8788.

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