• A CDC panel voted 13-1 to give health workers and long-term care facility residents the first COVID-19 vaccine doses once it's cleared for public use.
• There are roughly 21 million health-care workers and 3 million long-term care facility residents in the United States, according to a presentation during the CDC's Advisory Committee on Immunization Practices, an outside group of medical experts that advises the agency.

A Centers for Disease Control and Prevention panel voted 13-1 on Tuesday to give health-care workers and long-term care facility residents the first coronavirus vaccine doses once it's cleared for public use.

There are roughly 21 million health-care workers and 3 million long-term care facility residents in the United States, according to a presentation during the CDC's Advisory Committee on Immunization Practices, an outside group of medical experts that advises the agency. Dr. Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, said most states and local jurisdictions expect it to take three weeks to vaccinate all of their health-care workers. Pfizer and Moderna's vaccines require two doses about a month apart.

The meeting comes as states prepare to distribute a vaccine in as little as two weeks. Moderna and Pfizer have both requested emergency clearance from the Food and Drug Administration for their COVID-19 vaccines last month. The reviews by the FDA are expected to take a few weeks, and the agency has scheduled a meeting for Dec. 10 to discuss Pfizer's request for authorization.

Since the pandemic began, scientists and infectious disease experts have debated who will get immunized first and how the limited first vaccine doses will be distributed across the United States. Health and Human Services Secretary Alex Azar told CNBC on Nov. 16 that about 40 million doses of vaccine will available by the end of this year, enough to inoculate about 20 million people since the Moderna and Pfizer vaccines require two shots.

Earlier Tuesday, Trump vaccine chief Moncef Slaoui said the entire U.S. population of 331 million could be vaccinated against COVID-19 by June, and there could be enough doses to immunize the rest of the nearly 8 billion people in the world by early to mid-2022.

Read More: Trump COVID-19 vaccine chief Slaoui says everyone in U.S. could be immunized by June

The side effects from the vaccine can lay people up for a day or so, company officials have said. That's prompted officials to recommend that health-care facilities plan for workers to have time away from clinical care if they experience symptoms after getting vaccinated.

About 10% to 15% of people report noticeable side effects from the vaccines, according to Dr. Moncef Slaoui, who is leading the Trump administration's COVID-19 vaccine program Operation Warp Speed. The people who've suffered from side effects have reported redness and pain at the injection site as well as fever, chills, muscle aches and headaches, he said Tuesday, adding most people have no noticeable side effects.

Read More: Trump COVID-19 vaccine czar says side effects ‘significantly noticeable’ in 10% to 15% of recipients

Medical experts have previously advocated for health-care workers to get the vaccine first, followed by vulnerable Americans, including the elderly, people with preexisting conditions and essential workers. Children and young adults are expected to get the vaccine last.

Although states don't have to follow the CDC's guidance, it gives them a framework to work with and that many states adopt, Dr. Karen Landers, spokeswoman for the Alabama Department of Public Health, said in a recent phone interview.

"This guidance will be extremely helpful because it will be science-based, and also will give us the framework to be able to ensure that our guidelines are consistent with what is recommended by support staff," she said. "The Alabama Department of Public Health will follow those recommendations, and we'll certainly be following what ACIP recommends in terms of the vaccine administration.

The committee defined health-care workers as paid and unpaid people serving in health-care settings who have the potential for direct or indirect exposure to patients or infectious materials.

The group defined long-term care facility residents as adults who reside in facilities that provide a variety of services, including medical and personal care, to persons who are unable to live independently. Residents and staff in long-term care facilities account for 6% of COVID-19 cases but 40% of deaths in the U.S., according to the CDC.

During the meeting Tuesday, CDC officials said there is currently no data on how pregnant women will respond to Pfizer and Moderna's vaccines, which both use messenger RNA, or mRNA, technology. About 75% of health-care workers are women, according to a presentation during the meeting, and 330,000 of them are pregnant. Officials said they plan to provide further guidance on pregnant women once phase three trial data has been fully reviewed.

Drugmakers and states are gearing up to distribute the vaccine starting in mid-December. The Federal Aviation Administration said it supported the "first mass air shipment" of vaccines on Friday. United Airlines carried Pfizer's COVID-19 vaccine from Brussels to Chicago O'Hare International Airport on Friday, people familiar with the matter told CNBC.