2 COVID-19 vaccines report early positive results. So, what’s the difference between them?

2 COVID-19 vaccines report early positive results. 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.

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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.

Stop & Shop will be one of the first pharmacies in the country to administer COVID-19 vaccines. The company announced today it has signed a new partnership with the federal government. Boston 25 spoke with the clinical director for Stop & Shop pharmacies who says the ultra-cold storage needs will provide logistical challenges they really haven’t seen before.

“So much about the storage piece is up in the air, honestly," said Dr. Brittany Orlando, PharmD. “It’s probably one of the big logistical pieces, not just Stop & Shop, but logistically pharmacies, hospitals, doctors offices where a lot of us are not equipped with these extreme freezers to keep vaccines at these super, super low temperatures. That’s something that’s definitely been considered. Some preliminary information suggests that these vaccines may have a period of time, so a number of days or weeks, and they can be brought up into the standard freezer range or even the refrigerated temperature range. So, we’re working on the details of that to see how we’ll be able to offer it and store it appropriately.”

Both Moderna and Pfizer say they will file for emergency use authorization in the coming weeks. They say that it’s possible that, by the end of the year, some high-risk groups could receive the first round of the vaccines.

President Donald Trump said last week COVID-19 vaccines could be widely available in April. Moderna says summertime is a more feasible timeline, at least for their vaccine.

It remains to be seen whether any of the COVID-19 vaccines would require a booster or another round of vaccinations all together. Medical experts say that really will depend on how people react to them and how long the immunity lasts in real-world circumstances.

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