The 60 percent figure is people living their lives normally. Currently most people are social distancing, wearing masks and large gatherings have been cancelled

The 60 percent figure is people living their lives normally. Currently most people are social distancing, wearing masks and large gatherings have been cancelled. Under these circumstances 20 percent may well be herd immunity. But if Madison square garden was open and the subway was packed with people not wearing masks, its not clear that 20 percent would be enough.