Actually the CDC is predicting 550,000 by January. Not 1 million by December.
As for it being an over-estimate, look at the numbers...
The First case was 55 weeks ago. There are 8000+ cases now.
1,2,4,8,16,32,64,128,250,500,1000,2k,4k,8k
55 weeks/14 doubling cycles is 3.93 weeks per doubling cycle, every 27.5 days.
so the next doublings are
16k,32k,64k,128k,250k,500k,1m
7 cycles (192 days, 27 weeks) to reach 1 million.
2m,4m,8m,16m,32m,64m,128m,250m,500m,1b,2b,4b,8b
Another 13 cycles (358 days - 1 year) later, and it's the population of the planet.
(the current doubling rate depends upon the country, 15 days, 27 days and 30 days are the rate for the 3 worst countries)
All of this is based on NOT doing anything to stop it beyond what's been done so far. We are seeing some new things being done, so it won't be quite this fast.
I am not trying to take over this thread, and thought seriously that I should not post here. However, NO-ONE should take this lightly.
Honestly, if I hadn't just recently got married, I'd be in Botswana this year trying for a place.