Who gets the vaccine first and who decides? 3 things to know

With the Food and Drug Administration set to evaluate the two COVID-19 vaccine candidates in the coming weeks -- good news for a country fatigued by what seems to be a never-ending pandemic -- who will get the first doses?

On Tuesday, independent advisers to the Centers for Disease Control and Prevention will weigh in on that very question.

Once the FDA grants emergency use authorization, there will be a very limited supply of vaccine doses in the early stages of distribution. Given that, public health officials need to decide how to administer them equitably to the people who will be helped by vaccination the most.

Pfizer has said there will be about 6.4 million doses -- enough for about 3 million people -- available in the first shipments with more going out by the end of the year. Moderna, which submitted its application to the FDA this week, is expected to have 20 million doses immediately available if its vaccine is authorized. If both vaccines are authorized quickly there should be enough for 20 million people by the end of the year.

And as vaccine doses gradually become available to more Americans, state and federal governments face the challenge of communicating to the country it will still be necessary to wear masks, stay at home or social distance, and be vigilant about taking steps to limit the spread of the virus until the vast majority of the country is vaccinated.

Here are three things to know ahead of the CDC advisory committee meeting.

CDC advisers are discussing the ethics involved in deciding who gets the first doses

A CDC advisory committee on vaccines, called the Advisory Committee on Immunization Practices or ACIP, is scheduled to vote on who should receive the first round of COVID-19 vaccines.

The committee is made up of experts from around the country who make recommendations about how vaccines should be used, including who should receive certain vaccines and when, and the recommended schedule for vaccinating children. The members don't work for the government but provide independent expertise in how vaccines work, how the immune system responds, family medicine, and infectious diseases.

The committee, which has been meeting and discussing the best way to prioritize COVID-19 vaccines for months, is led by Jose Romero, chair of the Advisory Committee on Immunization Processes and Secretary of Health in Arkansas.

"What the ACIP wants to do is make sure that there is a fair, equitable and transparent distribution of these vaccines within the community, and that that the tiers we identify and we vote on represents the tiers that will get the best, the most benefit from a limited supply of vaccine initially," Romero told ABC News.

After the committee votes on its recommendations, they are then reviewed by CDC Director Robert Redfield and the Department of Health and Human Services and published by the CDC as guidance for states to determine their own plans.

In the case of vaccines not yet approved or authorized, the CDC committee typically makes its recommendations final after FDA weighs in, in part because FDA could put limitations on who can receive the vaccine under an emergency use authorization. For example, the FDA could say the vaccines are not appropriate for use in children under 12 because they don't have data on that age group yet.

HHS Secretary Alex Azar has said he will work with CDC so the FDA committee considering whether vaccines should be authorized and the CDC advisory group can meet at the same time so there are recommendations for how to distribute the initial doses of vaccine available as quickly as possible as shipments start to go out to states.

Health care workers likely to be the first to get vaccine in 'Phase 1a'

The planning for who can get vaccinated has been broken down into phases based on the amount of vaccine available at that time.

The very first round, referred to as "Phase 1a," has been mostly focused on health care workers treating COVID-19 patients and older adults living in nursing homes and long-term care facilities where the virus spread has been hard to contain and especially deadly.

The CDC committee and experts from the National Academies of Sciences, Engineering, and Medicine have also recommended that within each phase of vaccine distribution the government should prioritize reaching the parts of the country most severely affected by the virus first, which includes Black, Hispanic, and low-income communities.

"When we talk about, for example, in health care providers, we're not talking about just the doctors, nurses or respiratory therapists that are taking care of the patients in the hospital. We've expanded that to include the essential individuals that helped make the institution run," Romero told ABC News.

"So that would include, for example, the house cleaning staff that have to turn over the room very quickly to get the next patient in the emergency room, or clean the room for the individual that’s in the intensive care unit, the food delivery staff, the administration staff that are at the front desk of the emergency room."

He added "We look at those groups. We understand that underprivileged minority populations, lower-paid individuals are in that group. And so because of that, that expands the equitability of the recommendation."

States are ultimately in control of how they define the specific groups for each phase of the distribution and if they include other populations at high risk, such as first responders and people with conditions that put them at higher danger of serious illness from the virus.

Some states have already described their plans for who to include in Phase 1a distribution more specifically and submitted them to CDC, though they continue to be updated. In Arkansas, for example, the state's plan prioritizes health care personnel likely to be exposed to patients with COVID-19 as well as personnel providing COVID-19 testing or vaccinations, first responders, and essential government leaders.

As production and distribution of authorized vaccines ramps up states and public health agencies will expand who qualifies to get the vaccine, likely starting with essential workers and people more vulnerable to exposure to serious illness from the virus. Vaccines are expected to become available to the general public and lower risk individuals when there is enough supply to vaccinate the higher risk groups.

State governors and public health departments, not President Trump, will decide where the vaccines go

The FDA's determination that any vaccine is safe and effective is the first major step that has to happen at the federal level before any American can receive that vaccine outside of a clinical trial. Because the COVID-19 pandemic has created such an urgent situation, vaccine companies are applying for emergency use authorization, in which the FDA will authorize the vaccine for specific populations while companies and the agency continue to monitor people who receive it to get more data on potential side effects or how well it prevents people from becoming sick.

The federal government has worked for months with Operation Warp Speed, a combined effort through the Department of Health and Human Services and Department of Defense to distribute a vaccine quickly after the FDA makes a decision. But ultimately Operation Warp Speed will be taking its direction from states on how many doses need to go where and who will be vaccinated first in that state.

Azar and Army Gen. Gustave Perna, who is coordinating the shipments of vaccine doses and supplies, have said they will defer completely to states when deciding where vaccine shipments go.

"Our governors are like air traffic controllers. They'll tell us which hospital, which pharmacies, where they would like it to go. And they will be determining which groups to be prioritized," Azar said in an interview on "CBS This Morning" on Monday.

"I would hope that the science and the evidence will be clear enough that our governors will follow the recommendations that we will make to them, and we'll certainly call out any inequities or injustices that we see in approach. And we'll assess all of our options as we go. … I’ve got a lot of confidence in our governors to do the right thing here."

This report was featured in the Tuesday, Dec. 1, 2020, episode of “Start Here,” ABC News’ daily news podcast.

"Start Here" offers a straightforward look at the day's top stories in 20 minutes. Listen for free every weekday on Apple Podcasts, Google Podcasts, Spotify, the ABC News app or wherever you get your podcasts.