Moderna's vaccine does not require two doses, they administered two doses as part of their phase 2 trials to test for adverse reactions. They are only doing a single 100 µg dose for their phase 3 trials, and it's likely that will be the dose in the final vaccine:

https://www.fiercebiotech.com/biotech/moderna-finalizes-desi...

Moderna has plans to be able to manufacturer 1 billion doses a year. AstraZeneca has announced plans to manufacturer 2 billion doses a year, with plans to produce 300 million doses by the end of 2020. The Chinese firms Sinopharm and Sinovac are ramping up their production right now, and will produce 200-300 million doses by the end of 2020. With all the other firms developing a vaccine it seems highly likely we could produce enough vaccine to vaccinate the entire population of the Earth in a single year. Now distributing and administering that much vaccine is another story, but manufacturing will not likely be the bottle neck.