The only thing better than a COVID-19 vaccine is two COVID-19 vaccines. Now vaccines from both Pfizer and Moderna have received emergency use authorization from the Food and Drug Administration, with even more expected in 2021.

“Having two different brands of vaccine is incredibly important,” says Eric Arlia, Hartford HealthCare‘s System Director of Pharmacy. “Diversification of supply protects us all the more from any issues of disruption of supply.”

The Pfizer and Moderna vaccines are the first using a technology known as messenger RNA (mRNA). Rather than delivering a virus, these vaccines contain part of the virus’ genetic information that helps your body’s cells produce a viral protein that stops COVID-19. (A Hartford HealthCare Medical Group staff member, above, receives the Moderna vaccine in Wethersfield.)

Here’s a closer look at the two vaccines:

Age Restrictions

Pfizer: The FDA’s emergency use authorization applies to people 16 years old and up.

Moderna: 18 years old and up.


Pfizer: Two shots, a priming dose and a booster shot 21 days apart.

Moderna: Two shots, a priming dose and a booster shot 28 days apart.

How Well Does It Work?

Pfizer: In clinical trials, the vaccine developed by Pfizer and partner BioNTech was 95 percent effective at preventing COVID-19 infection.

Moderna: 94.1 percent effective from 14 days after the second dose.


Pfizer: Shipped and stored at minus-94 degrees. (Hartford HealthCare has purchased special freezers for this purpose.) Once thawed, the vaccine must be used within five days.

Moderna: Shipped at minus-4 degrees, a regular-freezer temperature. Once thawed, the vaccine remains stable in a refrigerator for 30 days and at room temperature for 12 hours.

“The Moderna vaccine represents a step in the right direction toward making a vaccine that easier to use in many different types of settings,” says Arlia. “Because this  vaccine stays stable in a refrigerator for 30 days, it really gives us a lot of additional options for the types of clinics we can use it in.”


Pfizer: Must be diluted with saline (salt water) before injection.

Moderna: Ready for injection from the vial. No dilution needed.

Side Effects

Pfizer: Some people experienced pain at the injection site, fatigue, muscle pain, headache, fever or joint pain. Four healthcare workers, two in the United Kingdom and two in Alaska, reported a serious allergic reaction. The National Institutes of Health says it’s preparing a study, expected to last a few weeks, to determine what component of the vaccine causes the reaction. But all these reactions are indicators of the immune system at work, not that the vaccines are unsafe.

Moderna: Similar to the Pfizer vaccine, though no reports of serious allergic reaction.

For more vaccine information, click here.

If you’re 75 or older and wanted to schedule your COVID-19 vaccine, log into your MyChartPlus account and find a Hartford HealthCare vaccine clinic near you. If you don’t have a MyChartPlus account, set one up here.