One key slide reveals who will be first in line to get a coronavirus shot in the US when a vaccine becomes available

• High-risk healthcare workers and first responders should be first in line for a coronavirus vaccine.
• The vaccine rollout should happen in four phases in the US, according to recommendations published in October by an expert committee.
• On Monday, Pfizer said that its experimental coronavirus vaccine was found to help prevent COVID-19. We could soon find out whether other leading vaccines work as well.
• The recommendations are widely expected to be adopted by the US government. Two public-health agencies asked the National Academy of Sciences in July to draft an allocation plan.

Healthcare workers at high risk of getting infected and first responders should be the first Americans to receive a coronavirus vaccine, if a shot becomes available.

An independent group of experts convened by the National Academy of Sciences issued their final recommendations in October on the question of who should get a COVID-19 shot first.

The US government isn't required to follow the group's recommendations but is widely expected to abide by them. The National Academy was requested in July to address the allocation question by two public-health agencies, the National Institutes of Health and the Center for Disease Control and Prevention.

The recommendations came before we got clinical results showing whether or not a vaccine candidate works in humans.

On Monday, Pfizer said that its experimental coronavirus vaccine was found to help prevent COVID-19, and other leading vaccines are expected to have results on whether the shots work in 2020 as well. Pfizer said it's planning to submit the vaccine for an emergency authorization in November. If regulators approve the vaccine, these guidelines will help determine who's first in line to receive it.

Read more: We could know if a coronavirus vaccine works in October. Here are the 7 most important events to watch for this month.

While the 237-page report goes into great detail on the rationale behind their recommendations, one graphic outlines the overall process Americans can anticipate.

The group outlined four phases for distribution, with certain sub-populations of the US gaining access to the shot as manufacturing ramps up. Demand for a vaccine will vastly exceed supply in 2020 and early 2021.

Phase 1 covers about 15% of the US population and focuses on the most vulnerable

The top priority will be for a COVID-19 vaccine to reach high-risk healthcare workers and first responders. People in this category cannot avoid exposure to the virus, as it's part of their essential jobs.

Healthcare workers doesn't just covers doctors, nurses, and dentists. Also included are nursing assistants and staff members at assisted-living facilities, group homes, and people providing home care.

First responders include police officers, firefighters, and emergency medical services workers.

This highest priority group makes up about 5% of the population. Moving beyond this so-called jumpstart phase, the initial rollout will then expand into people with underlying conditions that put them at significantly higher risk and the elderly living in nursing homes, homeless shelters, group homes, prisons, or jails.

Specific guidelines on age are left to the CDC to make at a later date, based on the most recent vaccine and health data, the committee's report says.

If vaccine doses are limited, as is widely expected, the group recommends focusing on people with two or more risk factors. These risk factors include cancer, chronic kidney disease, COPD, obesity, sickle cell disease, and type-2 diabetes, among other conditions.

The experts also acknowledge the uncertainty surrounding this list of risk factors, and notes this can and should change as more research is done on COVID-19.

Read more: 5 experts lay out how they'll determine whether a coronavirus vaccine is really safe and effective — here's what to know to evaluate the data for yourself

Phase 2 is an aggressive expansion, still focused on those who face more risk from COVID-19

The second tier would cover 30% to 35% of the country. When added to Phase 1, that means about half the nation should be vaccinated as part of these first two phases.

Phase 2 includes adults working in the school setting: school teachers, child care workers, administrators, environmental services staff, maintenance workers, and school bus drivers, according to the report.

It will also expand access to people working in vital jobs that cannot telework and avoid high risk of exposure. The report describes this group as people who "ensure that markets have food; drug stores have pharmaceutical products; public safety and order are maintained; mail and packages are delivered; and buses, trains, and planes are operating."

Additionally, anyone with at least one comorbidity that puts them at high risk to the virus would be included in the second phase. Also included are people who live in or work at homeless shelters, group homes, prisons, jails, and detention centers. Finally, Phase 2 includes any older adults who weren't included in the first wave of people.

Phase 3 and 4 expand to cover the rest of the nation

Phase 3 includes about 40% to 45% of the population, meaning the first three tiers combine to cover roughly nine in 10 Americans.

This group includes young adults between the ages of 18 and 30, children, and workers are increased risk of exposure not covered in the first two phases.

The committee prioritized 18- to 30-year olds because younger people have made up a significant chunk of viral spread, particularly noting this covers college students.

For children below the age of 18, the committee says it is "critical" to run pediatric trials before vaccinating kids. Vaccine trials enrolling kids have yet to start, although at least one leading developer expects to launch a pediatric study before year's end.

Phase 3 also shows a shift in priorities to consider social benefits from vaccination. Workers included in this tranche have jobs that "are important or desirable to maintaining the normal functioning of society." These include people who work in universities, restaurants, hotels, entertainment, banks, libraries, hair and nail salons, barbershops, and exercise facilities.

Finally, Phase 4 opens vaccinations up to anyone in the US who previously did not have access.

Read more: There are 176 coronavirus vaccines in the works. Here's how top drugmakers see the race for a cure playing out in 2020 and 2021 and when the first shots might be available.

This article was initially posted in October and has been updated with positive results from Pfizer's vaccine trial.