The first reported case came on January 21. Within 99 days, 1 million Americans became infected.
It took just 43 days after that to reach 2 million cases.
And 28 days later, the US reached 3 million cases of the novel coronavirus Wednesday.
1. BBC：对逃过死亡的新冠患者来说 一切仅仅是开始
2. 约翰霍普金斯大学：
