Huh? He specifically said : “But we are unsure right now what the protection is against infection”.
So yeah you were wrong when you claimed that he said “ It doesn’t prevent”. “We don’t know” and “We know it won’t” are NOT the same and we should take care not to confuse those concepts.
And by the way a new study today indicates it does prevent the vast majority of infections.
https://www.washingtonpost.com/health/2021/03/29/vaccine-effective-essential-workers-study/