Guidance recently released by the FDA outlining conditions for approving a Covid-19 vaccine includes a 50 percent benchmark, meaning that any vaccine must be at least 50 percent more effective than a placebo in preventing the disease. This is the same benchmark used annually to approve flu vaccines. In the announcement, Commissioner Stephen Hahn told a Senate panel that the FDA would not approve a vaccine for the general public without clinical evidence that it is both safe and effective.
In accordance with established FDA guidelines, an emergency authorization can move much quicker than a typical full approval, but would still require the vaccine maker to show through clinical studies that the vaccine produced lower levels of disease. Several clinical studies are underway, with one manufacturer having just initiated clinical testing by 60,000 adults.