It is the amount of time it takes to test it once developed. If the vaccine that will ultimately cure the virus was developed in February when the virus came to America, then the earliest you could expect it to hit consumption would be March or April of 2021. If it has yet to be developed, then youre looking at 13-14 months from whenever it is developed.

Chances are the vaccine has already been developed, they are just narrowing down which one is most effective without dangerous side effects from the ones currently in trials.