What is emergency use?
The FDA's power to authorize drugs for emergency use is relatively new, enacted by Congress in 2004 in response to the anthrax attacks of 2001.
The agency can grant such an approval if it is "reasonable to believe" that the product may be effective, and that its "known and potential benefits" exceed its "known and potential risks," according to the statute.
But vaccines are not like most drugs, in that they are administered to healthy people to prevent illness, not to treat it. So when the FDA issued guidance on what it would require before authorizing vaccines against COVID-19, the agency went beyond the letter of the law.
Drug makers learned they would need to enroll tens of thousands of participants, randomly assigning some to receive the vaccine and others to get a placebo. In short, they needed to run the type of large, well controlled trial that is required for regular approval of any vaccine, said biostatistician Susan S. Ellenberg, a professor emerita at the University of Pennsylvania's Perelman School of Medicine.
On Nov. 9, the partnership of Pfizer and BioNTech announced that its vaccine prevented more than 90% of cases of COVID-19, far exceeding most expectations.
Similar results came a week later from Moderna Inc., and by the middle of December, the FDA had authorized emergency use of both.
What more do they need?
Before granting the emergency authorizations, the FDA analyzed the rates of any side effects for two months following administration of the vaccines.
Any side effects caused by vaccines tend to arise within a month, and physicians generally agreed that two months' of safety data was more than sufficient — especially given the urgency of curbing the pandemic during the wintertime surge.