I don't think that it will be that delayed. Donald Trump was saying that he expect the vaccine to be available in the United States from this month onward. He also said that by December, the vaccine should reach the majority of the citizens there. Various European nations were also giving similar timelines. So by mid-2021, I expect most of the world population to be vaccinated.
Still uncertain that if in the first quarter of 2021 also we may have the vaccine available in the world, so till then there is no question of anyone getting it till the time it is confirmed the vaccine is being approved. Also once being approved how will the distribution happen will be the key.
WHO is not going to approve the vaccines unless Phase 3 trials are complete. And the issue here is that these trials involve tens of thousands of people and any indication of negative side effect reported from even one of these participants stalls the whole process. I believe China and Russia are doing the right thing, by approving the vaccine even before the Phase 3 trials are completed.