3 ms·
The original standard the CDC decided to use before we had data on any of the vaccines was that 50% protection would be the threshhold for "effective"; although
by gizmo686 5y ago
The original standard the CDC decided to use before we had data on any of the vaccines was that 50% protection would be the threshhold for "effective"; although I am not sure what level of infection they were planning on measuring (e.g. the vaccines appear more effective at preventing severe disease than symptomatic, and symptomatic than asymptomatic).