Smallpox used to kill millions every year. Here’s how humans beat it.
More than a million Americans have died of Covid-19, and the World Health Organization estimated this Thursday that the global death toll is around 15 million — a horrifying, and largely unnecessary, tragedy.
But for all that the world has lost in the last few years, the history of infectious disease has a grim message: It could have been even worse. That appalling death toll resulted even though the coronavirus kills only about 0.7 percent of the people it infects. Imagine instead that it killed 30 percent — and that…