But public fears that a vaccine is unsafe or ineffective could be disastrous, derailing the effort to vaccinate millions of Americans. DOING THE MATHThe FDA already has told manufacturers it won't consider any vaccine that's less than 50% effective. On the other hand, if equal numbers from the vaccine and placebo groups got infected, the DSMB might declare a vaccine futile, he told The Associated Press. These panels also can calculate infections even before that 150 threshold is met, at set time points in each study. Several vaccine candidates made by Chinese companies are in late stages of testing in various countries, but with smaller numbers of volunteers.

Source: ABC News September 09, 2020 14:26 UTC