After an expert panel of independent FDA advisors recommended on Friday against full approval of Pfizer and BioNTech’s booster, it is now up to the FDA to issue its official decision as to what groups, if any, will be eligible to receive the third dose. That announcement is expected to come this week.

The advisory panel voted 16-2 against a full-scale rollout of the booster to all Americans 16 and older. Favoring a more limited initial distribution of the booster, the panel voted 18-0 to recommend a third dose of the Pfizer vaccine for those who are 65 and older and for people who are either at high risk of contracting serious cases of COVID or work in places that make infection more likely.

Amid fears over waning vaccine immunity, spikes in new cases caused by the Delta variant, and a presidential promise of booster availability, the necessity of a third shot has become a debate that is seemingly once again both scientific and political.  

Should the FDA head the advice of its expert panel, booster jabs will be available to a much smaller population than the White House initially promised back in August. Of course, as Fortune healthcare reporter Sy Mukherjee wrote last week, the FDA could theoretically overrule the advice of its independent experts as it has done on several infamous occasions–– including when the agency green lit Biogen’s controversial Alzheimer’s treatment Aduhelm––and grant Pfizer a more wide-ranging authorization or approval. That would, however, be an extraordinary step in the context of a closely-watched pandemic and given the advisers’ recommendations for emergency use only in the high-risk and elderly.

An advisory committee of the Centers for Disease Control (CDC) is scheduled to meet on Wednesday and Thursday to discuss COVID booster shots before the agency itself issues its own recommendation on booster dosing and prioritization.

Beyond Pfizer, White House chief medical adviser Dr. Anthony Fauci said that the FDA will also be reviewing data on both the Moderna and Johnson & Johnson COVID booster shots in the coming weeks.

“The actual data that we’ll get [on] that third shot for the Moderna and second shot for the J & J is literally a couple to a few weeks away,” Fauci said on NBC News’s “Meet the Press” on Sunday. “We’re working on that right now to get the data to the FDA, so they can examine it and make a determination about the boosters for those people.”

The FDA’s ruling on the Pfizer/BioNTech booster could not only inform decision-making on the impending review of the Moderna and Johnson & Johnson booster shots but could also determine how regulators approach future boosters needed for any potential mutations of the virus down the line.

White House officials said on Friday that the United States was ready to roll out booster shots this week had regulators approved the third dose. The White House’s original plan preempted any action taken by the FDA, leading to several prominent resignations at the agency over perceived political meddling in early September.

While the FDA’s advisory panel has initially recommended a narrow distribution of the booster, health officials such as National Institutes of Health Director Dr. Francis Collins believe that it’s only a matter of time before broader use is approved.

“I’m not sure about absolutely everyone,” Collins said on “Fox News Sunday” when asked whether he thought the booster would be needed for everyone. “We’ll have to see what they say ultimately about the youngest individuals because of concerns about benefits and risks, but, I will be surprised if boosters are not recommended for people under 65 going forward in the next few weeks. But we’ll wait and see.”

Of course, regardless of what any of these regulatory agencies rule, there’s no guarantee that the general public will respect the limitations placed upon who is eligible to receive a booster. As Mukherjee noted last week, many Americans have taken it upon themselves to secure booster shots despite being ineligible to do so, and at least 1 million people had already gotten an extra dose before any had been authorized by the FDA, according to CDC estimates.