The effect needs to be strong, because in ordinary times, many social circles cross paths and a much higher level of human contact occurs. The average person wo

The effect needs to be strong, because in ordinary times, many social circles cross paths and a much higher level of human contact occurs. The average person won't read into the nuance of 'the vaccine is X% effective, depending on risk factors Y and Z'. They'll rush to their ordinary behavior. While there isn't a vaccine, it's easier to obligate folks into social distancing. That strategy won't exist anymore once we have a vaccine, regardless of its efficacy.