The Centers for Disease Control and Prevention's advisory committee voted 13-1 on who would receive the vaccine in groups "1b and 1c" and who would be "essential."

Phase 1b includes people over 75 and front-line essential workers, while phase 1c includes younger patients with high-risk medical conditions and other essential workers.

Those two groups would cover K-12 teachers, school staff, child care workers and critical workers in high-risk settings.

It would also include people in homeless shelters, prisons, jails, detention centers and mental development centers and staff who work in these places, according to the CDC.

The committee also defined front-line essential workers as first responders, educators, food and agriculture workers, manufacturing workers, corrections workers, U.S. postal workers, public transit workers and grocery store workers.

The front-line essential workers represent about 30 million Americans, according to the CDC.

The CDC is expected to sign off on these recommendations to make the next phase of vaccines available to Americans over 75 and front-line workers, but it will ultimately be up to states to define which front-line workers qualify.

-ABC News' Adisa Hargett-Robinson and Stephanie Ebbs contributed to this report

Half a million Americans received Pfizer vaccine in first week: CDC

The Centers for Disease Control released its first set of data on the Pfizer coronavirus roll out.

As of Sunday afternoon, at least 556,208 doses have been administered and 2.8 million doses have been distributed throughout the country, according to the CDC.

The first doses were given out to hospital workers, nursing home staff and federal elected officials starting on Dec. 14. Those patients will need a second dose in a few weeks.

The CDC told ABC News it plans to transition this data to agency's COVID Data Tracker in the next couple weeks and have data available down to the jurisdictional level.

A coronavirus vaccine manufactured by Moderna began shipping on Sunday and is slated to be administered this week.

-ABC News' Eric Strauss contributed to this report.

The second COVID-19 vaccine to be authorized by the FDA is now being rolled out.

The first cases of the Moderna vaccine were seen being rolled out from a facility in Olive Branch, Mississippi, to be shipped to the FedEx hub in Memphis, Tennessee, for nationwide distribution on Sunday morning. The shipment was escorted by U.S. Marshalls.

The doses were packed into insulated coolers with specialized cold packs and a temperature monitor, according to pharmaceutical distribution compant McKesson.

The initial vaccine orders will be delivered to administration sites on Monday.

ABC News’ Gio Benitez and Ahmad Hemingway contributed to this report.

Health care company McKesson Corporation has begun distributing Moderna’s COVID-19 vaccine and the ancillary supply kits needed to administer it, they said in a statement Sunday.

Brian Tyler, the CEO of McKesson, said, “We are honored to be a partner with the U.S. government and other private-sector companies such as Moderna to support in the distribution of COVID-19 vaccines and the ancillary supply kits."

Their vaccine distribution plan, they said, is part of Operation Warp Speed's effort to distribute COVID-19 vaccines to all Americans, and under the direction of the Centers for Disease Control and Prevention (CDC).

"In March, our world seemed to change overnight," Tyler added. "But with a renewed sense of commitment and intensified focus, we’ve come together across industries and forged public and private partnerships to help restore and protect the health and wellbeing of people around the world. With our exceptional group of employees managing the effort, we stand ready as a company to meet this historical moment.”