Felicia Wu, a John A. Hannah Distinguished Professor at Michigan State University, said in this great article:
The Los Alamos study estimated that 82% of the community needs to be immune to the novel coronavirus before all public health restrictions can be lifted, because their estimated R0 for SARS-CoV-2 is so high. The United States has a population of approximately 328 million people, so about 268 million people would have to develop immunity to the novel coronavirus in order to safely go out in society. Herd immunity for the seasonal flu is 55%.