Comparing the Pfizer and Moderna COVID-19 vaccines

With front-line doctors receiving the Pfizer vaccine and Moderna's vaccine on the cusp of authorization by the Food and Drug Administration, Americans may be wondering: What's the difference between the two?

The short answer: The vaccines are more alike than they are different, especially for members of the general public.

Here's what we know so far:

The similarities:

Both vaccines utilize mRNA, or messenger RNA, technology, meaning they teach cells to make a protein that prompts an immune response.

Both Pfizer and Moderna's vaccine have proved remarkably effective in trials, with more than 94% efficacy rates for protecting against COVID-19. The vaccines were both effective for different races and genders, as well as for people with underlying medical conditions.

Side effects for both the Pfizer and Moderna vaccine were generally mild and temporary, including pain at the injection site, headache, fever, fatigue, chills and muscle and joint pain.

The differences:

The differences between the Pfizer and Moderna vaccines may matter most to the people tasked with transporting and storing them.

While both vaccines are stored at cold temperatures, Pfizer's needs a special freezer to keep the vaccine at minus 94 degrees, while Moderna's vaccine can be kept in a regular freezer at minus 4 degrees.

The companies' vaccines are also authorized for slightly different age groups. Pfizer's vaccine is authorized for people 16 years old and up, while Moderna's authorization request includes people 18 and older.

The vaccines' two-dose timelines are slightly different. Pfizer's shots are scheduled to be given 21 days apart, while Moderna's have a 28-day spread.

In the end, the subtle differences won't be a major factor for most Americans, since it's very unlikely people will get to choose which vaccine they get, Dr. Jill Weatherhead, an infectious disease professor at Baylor College of Medicine told Houston ABC station KTRK.

Instead, whether people are offered a Pfizer or Moderna vaccination will likely depend on which is available in their area.

What to know about the coronavirus:

• How it started and how to protect yourself: Coronavirus explained
• What to do if you have symptoms: Coronavirus symptoms
• Tracking the spread in the U.S. and worldwide: Coronavirus map

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This report was featured in the Friday, Dec. 18, 2020, episode of “Start Here,” ABC News’ daily news podcast.

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