FORT WORTH (CBSDFW.COM) – The U.S is on the verge of having two approved vaccines for COVID-19.

Hospitals in North Texas have been administering the Pfizer vaccine this week to frontline healthcare workers, and the FDA could greenlight the Moderna shot as soon as Friday, Dec 18.

“We are giving shots 16 hours a day, seven days a week,” said Dr. Joseph Chang, chief medical officer at Parkland Hospital, which received more than 5,8000 doses of Pfizer’s vaccine. “I’ve never seen people happy to be in a line like that, and I’ve been to Disney World many times.”

The first Pfizer shipments arrived this week at North Texas hospitals.

The state expects to receive even more in the coming weeks, with the Moderna vaccine on track to get emergency use authorization from the FDA.

The two vaccines are very similar.

Both are messenger RNA vaccines, which means they don’t contain the live virus.

“Both of them are thought to be approximately 95%, effective, and both will also require that you have two doses,” said Dr. Meenakshi Ramanathan, an associate professor of pharmacotherapy at the UNT Health Science Center College of Pharmacy.

Pfizer’s second dose is administered 21 days after the first; Moderna’s second dose is administered 28 days after the first.

They can’t be mixed.

“You can’t get Pfizer first and then Moderna second, or Moderna first and Pfizer second,” said Dr. Ramanathan. “It doesn’t work that way.”

Both shots have side effects you’d expect from a vaccine.

“It’s thought with the Moderna vaccine, the second dose is actually where you’ll see more of these types of reactions – headache, fever, fatigue, flu-like symptoms, et cetera,” she said.

A big difference between the two is how they’re stored. Pfizer’s needs a deep freezer, while Moderna’s can be kept in a standard one.

The Texas Department of State Health Services says the Moderna vaccine will allow smaller and rural providers to get allocations.

“Because of our ability to store ultra-cold items, we will probably be getting mostly Pfizer because not everyone can do that,” said Dr. Chang. “And so some of the other places that cannot do that more likely maybe get the Moderna vaccine.”

Experts say it’s unlikely people will be able to choose which vaccine they get. It will depend on what’s available in their area.

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Caroline Vandergriff