More than 60 percent of American adults have received at least one vaccine shot, and the share is growing by about two percentage points per week. Among unvaccinated people, a substantial number have already had Covid and therefore have some natural immunity. “The virus is running out of places to be communicable,” Andy Slavitt, one of President Biden’s top Covid advisers, told me. The share of Covid tests coming back positive has fallen below 3 percent for the first time since widespread testing began, and the number of hospitalized patients has fallen to the lowest point in 11 months, Dr. Eric Topol of the Scripps Research Translational Institute noted. For the first time since March 5 of last year, San Francisco General Hospital yesterday had no Covid patients — “a truly momentous day,” Dr. Vivek Jain said... But the sharp decline in cases over the past month virtually guarantees that deaths will fall over the next month. The pandemic appears to be in an exponential-decay phase, as this helpful Times essay by Zoë McLaren explains. “Every case of Covid-19 that is prevented cuts off transmission chains, which prevents many more cases down the line,” she writes.