As the possibility of a widely available COVID-19 vaccine steadily approaches, initial limitations in supply have left experts worldwide asking: Who gets the vaccine first?

The World Health Organization and its appointed Strategic Advisory Group of Experts on Immunization, or SAGE, have released a worldwide vaccine distribution plan -- it pushes back on so-called vaccine nationalism, the idea that each country should prioritize its own citizens.

Instead, the WHO touts a global approach, prioritizing vaccination among the most vulnerable people everywhere.

"The first priority must be to vaccinate some people in all the countries, rather than all the people in some countries," WHO Director-General Dr. Tedros Adhanom Ghebreyesus said in Geneva on Friday. "Vaccine nationalism will prolong the pandemic, not shorten it."

The WHO's proposed vaccine distribution framework ensures all countries access to the novel coronavirus vaccine once it becomes available. Participating upper- and middle-income countries, also called "self-financing" countries, will provide funding for the vaccine accelerator program, abbreviated COVAX, knowing that the long-term goal is global prosperity.

Seventy-eight wealthier countries have endorsed the program, with Germany, Japan, Norway and the European Commission this week expressing an interest in participating in the COVAX facility as self-financing countries. So far, a total of 170 nations intend to participate in COVAX, representing about 70% of the world's population. The United States is not among them.

"The idea behind the COVAX facility is that the world community unite in an enlightened and self-interested way to both incentivize and then distribute the vaccine so that there's no country in the world where no vaccines are available right from the beginning," said Dr. Ruth Faden, Ph.D., M.P.H., founder of the Johns Hopkins Berman Institute for Bioethics. "The countries that come in who are self-financing are essentially helping themselves by helping the world."

In addition to strategizing an equitable distribution strategy among countries, the WHO's framework also examines vaccination priorities within each country.
MORE: Vaccine nationalism: Experts warn countries against taking 'me-first' approach

By comparison, last week a committee that advises the U.S. Centers for Disease Control and Prevention proposed four sequential phases of vaccine prioritization within the U.S., beginning with high-risk health care workers, people with serious medical conditions and seniors living in crowded facilities.

The WHO guidelines don't include the order in which certain groups would receive the vaccine, but the plan does highlight certain vulnerable groups as a higher priority for global impact, with some flexibility based on each country's unique needs.

"We specifically did not say which groups should be prioritized first, second and third. That will come later. Not too long from now, but that will come later," continued Faden, who consults as a member of the working group that helped draft the framework but does not represent the international agency.

Local transmission patterns, the general quantity of vaccine supplies and a nation's infrastructure all will influence distribution tactics, Faden added. These will likely change between now and when a vaccine is approved, so as more information becomes available, the SAGE group will then begin prioritizing specific groups.

The framework's flexible approach is perhaps exemplified in the way children will be considered for vaccination.

"There's tremendous focus in our values structure around the negative impact that the pandemic has had on the well-being of children -- there's 1.5 billion kids out of school," Faden said. "It's just staggering, globally, the number of children whose lives have been disrupted. The goal is to get kids in school, full time, as quickly as possible.

"As the vaccine becomes available, it may be that the first-line strategy is to vaccinate teachers and school staff and not children, if only because the data will come first in adults."

In the United States, Pfizer/Biontech recently announced plans to expand testing to adolescents as young as 16.

"The WHO framework is particularly notable for its emphasis on global equity," Faden explained, "with specific objectives aimed at wealthy countries. ... The framework considers not only the public health impact of vaccine allocation, but also the social and economic impacts."

Dr. Dave Harrison is a pediatric cardiology fellow in Boston and a contributor to the ABC News Medical Unit. Sony Salzman, the unit's coordinating producer, contributed to this report.