But Fauci warned that widespread distribution and getting “the majority, or more, of the population vaccinated and protected” won’t happen until perhaps the end 2021,
One of the reasons for this is the government lacks a whole lot of pressure points for forcing vaccinations (short of rounding people up on the street and dragging them into the doctor's office as Australia has floated). With right and left lining up to not take a vaccine developed by the other side, this fight is looking uglier by the day. The rationale for that date is it looks like pediatric doses won't be available until the spring at earliest (though one of the trials recently did drop enrollment as low as 16 year olds). One of the easiest and proven ways to boast immunization rates is by requiring kids to take it for school. So the pressure point is August of 2021 when it will be required for kids to return to school. Since its looking 2 doses separated by weeks are required, that's where you get the date from.
Other pressure points like going into a hospital or a nursing home might take time to build as new people gradually go into nursing homes and hospitals. Some like the military or large corps voluntarily requiring it to return to the office will help but don't make up the numbers. The kids are a quick way to get the numbers up. Some ideas being floated (like requiring proof of immunization to fly) may or may not take.