“The intensity and speed with which it struck were almost unimaginable — infecting one-third of the Earth’s population,” the World Health Organization said.
Fast-forward to 2020, and the novel coronavirus is also spreading with astonishing speed.
Some of the painful lessons learned from the 1918 pandemic are still relevant today — and could help prevent an equally catastrophic outcome.
Lesson #1: Don’t let up on social distancing too soon
During the Spanish flu pandemic, people stopped distancing too early, leading to a second wave of infections that was deadlier than the first, epidemiologists say.
In fact, one large gathering near the end of the first wave in 1918 helped fuel the deadlier second wave.
In San Francisco, when the number of Spanish flu cases was almost down to zero, “the city fathers said, ‘Let’s open up the city. Let’s have a great big parade downtown. We’ll all take off our masks together,'” epidemiologist Dr. Larry Brilliant said.
“Two months later, because of that event, the great influenza came back again roaring.”
On the other side of the US, Philadelphia suffered a similar fate.
Even though 600 sailors from the Philadelphia Navy Yard had the Spanish flu in September 1918, the city didn’t cancel a parade scheduled for September 28, 1918.
“Quickly, Philadelphia became the city with the highest influenza death toll in the US,” Penn research states.
By contrast, St. Louis — which scheduled a similar parade but canceled it — fared much better.
Of course, different places will reach different peaks at different times. But just because one place moves past a so-called peak with coronavirus doesn’t mean cases or deaths there can’t rise again.
“The image that we have of this epidemic curve, we say we’re going to reach a ‘peak’ — we look at it, it looks like Mt. Fuji in our minds … a single, solitary mountain,” Brilliant said.
“I don’t think it’s going to look like that. I think a better image is a wave of a tsunami, with echoed waves that follow. And it’s up to us, how big those other waves will be.”
Lesson #2: Young, healthy adults can be victims of their strong immune systems
About two-thirds of the deaths then were among people ages 18 to 50, “and the peak age for death was 28,” said Barry, author of “The Great Influenza: The Story of the Deadliest Pandemic in History.”
One reason the 1918 flu was so deadly for young adults was because the outbreak started during World War I, when many soldiers were in barracks and in close proximity with each other.
“The US military training camps obviously had high mortality,” Barry said.
There’s no world war now, but important lessons remain: Young, healthy people are not invincible. And their strong immune systems might work against them.
“In some young, healthy people, a very reactive immune system could lead to a massive inflammatory storm that could overwhelm the lungs and other organs,” Gupta said.
“In those cases, it is not an aged or weakened immune system that is the problem — it is one that works too well.”
Lesson #3: Don’t throw unproven drugs at the virus
Yes, there have been major medical and technological advances in the past 102 years. But the Spanish flu and the novel coronavirus pandemics share two major challenges: the lack of a vaccine and the lack of a cure.
“This provides evidence that hydroxychloroquine does not apparently treat patients with Covid 19,” said Dr. Paul Offit, an infectious disease specialist at Children’s Hospital of Philadelphia.
“Even worse, there were side effects caused by the drug — heart toxicities that required it be discontinued.”
The bottom line: It’s still not clear whether some drugs will cause more harm than good in the fight against coronavirus.
CNN’s Leah Asmelash, Elizabeth Cohen and Dr. Minali Nigam contributed to this report.