Trump is being very optimistic. He is not guaranteeing anything. The dumb press hangs on his every word in playing “gotcha” and the people are tired of their petulance.
I think Trump knows this virus is going to burn itself out before a vaccine can be ready. But there is no way he can tell the Karens that. So he plays along with the Great Vaccine Hope.
I think he as information on the Oxford study. He most certainly would know of Moderna’s numbers. The press doesn’t think Trump gets information that is pertinent to national security apparently. Given that he is yet to be wrong, I am not inclined to think he will start now being incorrect.