DALLAS (NewsNation Now) — It has been a hopeful couple of weeks with two consecutive Fridays with FDA approval of COVID-19 vaccines, and now it is the second Monday that we’re seeing those shipments make their way to healthcare facilities across the country.

The Moderna vaccine officially rolled out Monday morning. It is the second weapon in the country’s coronavirus arsenal. Moderna’s vaccine is making its way down factory conveyor belts in Kentucky and Mississippi and into the hands of delivery drivers and airliners for transport across the country.

Just last week, the world watched as America’s first frontline workers received the Pfizer vaccine.

The immunizations work similarly. Both use a double-dose of messenger RNA technology to produce antibodies, both are about 95 percent effective and each is taken about a month apart.

“They work for all practical purposes the same way, but they’re not interchangeable,” said Dr. Joseph Gastaldo, an infectious disease specialist for OhioHealth System. “So it’s another layer of complexity of us having to do two different vaccines.”

The biggest difference comes down to storage. While Pfizer has to be kept in a sub-zero unit, Moderna’s vaccine can be kept in any pharmacy-grade freezer.

“It (Moderna) does not require the ultra-cold storage, so it’s going to lend itself much better to use in pharmacies, rural communities and other places that don’t have the ability to keep a vaccine in ultra-cold storage,” said Dr. Dale Bratzler, the chief COVID officer for the University of Oklahoma.

By the end of December, Moderna says it will have shipped approximately 20 million domestic doses. About 125 million doses are expected globally in the first quarter of 2021. Americans will watch and wait to see if those numbers hold true.

Over the weekend, the chief operating officer of Operation Warp Speed apologized after multiple states reported receiving far fewer Pfizer vaccines than anticipated.

“And I want to take personal responsibility for the miscommunication,” said Army General Gustave Perna. “I know that’s not done much these days, but I am responsible.”

The first allotment of the Moderna vaccine is still headed to prioritized healthcare workers. Many like nurse Mandy Delgado with Hartford Hospital stepping forward not only for personal protection, but also to allay fears.

“It’s important to me because I feel like there’s a lot of hesitancy in my community about getting this vaccine, and I want people to feel comfortable getting the vaccine knowing that it is okay,” said Delgado. “This vaccine is safe.”

The vaccine isn’t just welcome news for healthcare workers, but also those considered high-risk if they were to contract COVID-19.

Chris McMahon, 52, of Georgia, was one of 30,000 patients who participated in the Moderna trial this summer.

“If I did get COVID-19, it’s basically like an 80-year-old person getting it. That’s my vulnerability,” said McMahon, who has type-1 diabetes. After his endocrinologist recommended he take part in the trial, he listened.

McMahon’s first dose was in May and his second in June.

“I did have soreness at the location of injection,” he said. “And then kind of a very flu-feeling for the next three days. If I would have gone to get a tetanus shot, I probably would’ve had the same thing.”

Hospital officials that NewsNation checked with said that whichever brand of vaccine a facility starts with is the one it will continue to receive, as the doses are not interchangeable.