Food and Drug Administration (FDA) Commissioner Stephen Hahn told the Financial Times in an interview published Sunday that the agency is willing to issue an emergency use authorization (EUA) for vaccines that protect against the novel coronavirus before phase 3 clinical trials for the vaccines are complete. He noted, however, that a final decision will ultimately be based on the data that's submitted by drugmakers.

One of the main differences between an EUA and a full approval is that the former only lasts as long as an emergency continues. Because it's temporary for a specific emergency, an EUA has a lower threshold for the calculation of benefit versus risk. One way the FDA might mitigate the unknown risk is by authorizing the use of the vaccine in only high-risk populations -- healthcare workers, for example -- until the full phase 3 data are available.

A child receiving a shot in the upper arm

Image source: Getty Images.

Pfizer (PFE -0.13%) and BioNTech (BNTX -2.04%) have indicated that they hope to submit data on their coronavirus vaccine to the FDA by October. Considering the time needed to conduct trials, it's unlikely the companies will have the full phase 3 data set by then. Last week, Pfizer's management noted that the study is more than 50% enrolled, but that means the companies still have nearly 15,000 patients left to enroll. Patients need to get a booster shot 21 days after the first dose, at which point the companies can start measuring whether the vaccine reduces the likelihood of coronavirus infection compared with placebo.

The first patients who enrolled in the study when it started in late July will have already received their booster shot, allowing for an efficacy measurement in October. But it seems unlikely there will be much, if any, data on the patients enrolled toward the end of the study at that point.

Moderna (MRNA -0.12%) is in a similar situation, having enrolled almost 17,500 patients into its 30,000-patient phase 3 study as of Friday.