In 1918, a novel strand of influenza killed more people than the 14th century’s Black Plague.

At least 50 million people died worldwide because of that H1N1 influenza outbreak. The dead were buried in mass graves. In Philadelphia, one of the hardest-hit cities in the country, priests collected bodies with horse-drawn carriages.

In the middle of today’s novel coronavirus outbreak, some are turning to the conclusion of past pandemics to discern how and when life might “return to normal.” The Washington Post has received a few dozen questions from readers who want historical context for our current epidemic. But how did the deadliest pandemic ever recorded come to an end?

Over time, those who contracted the virus developed an immunity to the novel strand of influenza, and life returned to normal by the early 1920s, according to historians and medical experts. Reports at the time suggest the virus became less lethal as the pandemic carried on in waves.

But the strand of the flu didn’t just disappear. The influenza virus continuously mutated, passing through humans, pigs and other mammals. The pandemic-level virus morphed into just another seasonal flu. Descendants of the 1918 H1N1 virus make up the influenza viruses we’re fighting today.

“The 1918 flu is still with us, in that sense,” said Ann Reid, the executive director of the National Center for Science Education who successfully sequenced the genetic makeup of the 1918 influenza virus in the 1990s. “It never went away.”