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Side-by-side: How Pfizer, Moderna COVID-19 vaccines compare

While both are two-dose vaccines that are above 90-percent effective, the difference will be how they're stored.
Credit: 10 Tampa Bay
Clinical trial data released for both Pfizer and Moderna vaccines

TAMPA, Fla. — Within weeks, both Pfizer and Moderna have risen to the top in the race for a COVID-19 vaccine.

"It's really exciting to have two candidates out there! Their trials were very similar," Dr. Jill Roberts with USF Public Health said. 

The infectious disease expert explains both vaccines are banking on new technology to fight the virus. It's called mRNA and no vaccine has previously used the method and been approved by the FDA before.

"They're both mRNA. This is looking at the nucleic acid level, the real way that these viruses will replicate. So it's exploring a system that's really new," Roberts said. 

The vaccines target the spike protein the COVID-19 uses to attack cells. Once the cells are stimulated, nontoxic versions of the spike protein are produced and trigger an immune response.

"We were hoping that a vaccine would be 50 percent efficacious. Looking like in the preliminary data, it's more like 90 percent. That's absolute greatness," Dr. Kami Kim with USF's Morsani College of Medicine and Tampa General Hospital said.

In Pfizer's clinical trial, 94 out of almost 44,000 trial participants got sick with COVID-19, making the two-dose vaccine 90 percent effective.

For Moderna, 95 of 30,000 got the virus. All but five people were given a placebo, meaning the protection from COVID-19 is 94.5 percent.

While both are two-dose vaccines, the difference will be how they're stored.

"Moderna is really touting that their vaccine actually might be more stable than Pfizer's is and why that's important is because the vaccines require refrigeration. There's a lot of places already scrambling saying, 'Okay well, we're going to get this vaccine, but how are we going to keep it refrigerated?' That's been a long time issue," Roberts said.

Data shows Moderna's vaccine will remain stable for up to 30 days at 36-46 degrees Fahrenheit. That's the temperature of your standard freezer or medical refrigerator. 

Pfizer's vaccine will need a storage temperature of -94 degrees Fahrenheit.

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