Sometimes, the most confusing part of Covid-19 is when the spread slows down. We’ve learned a lot about how the virus spreads, but in places like NYC, are we also getting key clues about when the curve flattens? And are those clues suggesting that herd immunity might come at a lower infection rate than we thought? (Or are these just breaks between the waves?) What if Herd Immunity Is Closer Than Scientists Thought? “To achieve so-called herd immunity — the point at which the virus can no longer spread because there are not enough vulnerable humans — scientists have suggested that perhaps 70 percent of a given population must be immune, through vaccination or because they survived the infection. Now some researchers are wrestling with a hopeful possibility. In interviews … more than a dozen scientists said that the threshold is likely to be much lower: just 50 percent, perhaps even less.”