Promising Phase Three clinical trial data from two companies leading the vaccine race could be the beginning of the end of the coronavirus pandemic—but hurdles to approval remain.

Next steps in the hastened timeline relate to the Food and Drug Administration authorizing emergency use to one or more vaccine candidates. The FDA set a minimum effectiveness bar at 50% efficacy for vaccine makers aiming to submit their candidates for emergency authorization.

Drug makers Pfizer and Moderna recently announced their coronavirus vaccines are more than 90% and 94% effective, respectively.

If the vaccines receive the FDA greenlight, the first doses could be distributed in December. Once available, health care workers, essential workers and those at higher risk of severe complications from COVID-19 will receive the vaccine first. That could cover potentially 20 million people, likely around mid-December.

Still, the FDA could take weeks to review the clinical data and approve vaccine production facilities. FDA officials have voiced concerns that granting emergency authorization use would inhibit long-term assessment of safety and efficacy in ongoing trials, precluding the drug-makers from applying for full license in the future.

With many Americans still hesitant about a coronavirus vaccine, about a half-dozen (mostly Democrat-led) states and the District of Columbia have established committees to review coronavirus vaccine candidates offered for FDA approval.

Policymakers will decide how many doses of the coronavirus vaccine are sent to each state. However, states will be individually tasked with distributing the vaccine, with little guidance or funding from the federal government once it is made available.

Public appetite will play a part as well. According to recent polling, nearly half (48%) of Americans say they would trust a Moderna vaccine somewhat or a lot, while 27% of Americans say they would not trust it very much or at all.