One year ago, the biggest vaccination drive in American history began with a flush of excitement in an otherwise gloomy December. Trucks loaded with freezer-packed vials of a COVID-19 vaccine that had proved wildly successful in clinical trials fanned out across the land, bringing shots that many hoped would spell the end of the crisis. The nation’s COVID-19 death toll stands at around 800,000 as the anniversary of the U.S. vaccine rollout arrives. An untold number of lives, perhaps tens of thousands, have been saved by vaccination.