2 COVID-19 vaccines now approved. So, what’s the difference between them?

BOSTON — There are a couple of small differences between the Pfizer and the Moderna COVID-19 vaccines and at least one big one.

First, is their rate of effectiveness. Pfizer reported last week their vaccine was 90% effective.

Moderna, on Monday, reported a rate of 94.5% efficacy.

Both efficacy rates are considered very good news.

  • MODERNA 94.5% effective
  • PFIZER 90% effective

Both vaccines require two doses, 21 days apart for Pfizer and 28 days for Moderna.


PFIZER: 2 doses, 21 days apart

MODERNA: 2 doses, 28 days apart

The biggest difference in these two vaccines is what’s required to store them. Both require cold storage, but Moderna’s is a little more flexible.

Moderna reports its' vaccine is stable at 36-46 degrees Fahrenheit, the temperature of a standard home or medical refrigerator, for 30 days. And, they say it can be kept at room temperature for up to 12 hours.

Pfizer’s vaccine has to be stored at ultra-cold temperatures: minus 94 degrees Fahrenheit. That requires special medical freezers that can reach that level. Those are rare, even in wealthy nations like the United States.

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