Read: The deceptively simple number sparking coronavirus fears

Twitter ate it up. Many people seemed to be experiencing the outbreak, especially from afar, as some kind of distributed movie, watched in grainy cellphone videos sent out of China and populated by Twitter heads filling in the backstory. The thread soon had thousands of retweets. Feigl-Ding’s account was flooded with new followers. Here was a Harvard epidemiologist naming the world’s darkest fear about the new disease and confirming it.

Yet there were issues with Feigl-Ding’s analysis, even if they were not immediately apparent to the people simply scrolling through Twitter. The thread exemplified a deep problem on Twitter: The most extreme statements can be far more amplified than more measured messages. In the information sphere, while public-health researchers are doing their best to distribute scientific evidence, viral Twitter threads, context-free videos, and even conspiracy theories are reaching far more people.

The coronavirus outbreak is a serious public-health problem. Although reports began to surface in early January, the Chinese government massively escalated its response last week, calling for an unprecedented quarantine of tens of millions of people. The outbreak struck within a fraught set of geopolitical circumstances. There is the history of the respiratory illness SARS. There is the uncertainty about how transparent the factions of the Chinese government are being about the severity of the outbreak. There is the sheer size of China—and the appearance of the disease in the weeks leading up to the new year, which sends hundreds of millions of people traveling across the country. And, of course, there is global competition between the U.S. and China, which provides a little extra incentive (and prospective attention) for Americans on Twitter trying to garner an audience.

Most Americans cannot read Chinese, nor are they present in large numbers on Chinese social-media sites such as Weibo and WeChat. The internet has fractured over the past decade, with American and Chinese social-media companies carving up distinct parts of the world. While that makes it difficult for many Americans to parse what’s happening on Chinese social media, it also creates an opportunity for people who are tapped in on both sides. They can arbitrage from the Chinese to the American internet, turning WeChat videos into Twitter gold. Accounts big and small have whipped up quite an apocalyptic fervor in the past weeks, posting scary videos of dubious provenance and veracity. The mainstream media has proceeded carefully, and reporters’ stories have seemingly been unable to satiate the rising hunger for more information about coronavirus.

This was the ecosystem in which Feigl-Ding’s thread landed. No wonder it took off. Unfortunately, there were some mistakes. While Feigl-Ding included quotes and screenshots of the paper, which was preliminary and not peer-reviewed, he omitted some context, primarily that other infectious diseases such as measles also have very high R0 numbers. He also made a clear error: “Ding claimed that the new virus was eight times as infectious as SARS, when in fact SARS had an R0 ranging from 2 to 5, very comparable with these estimates for the new coronavirus,” the science journalist Ferris Jabr, who watched Feigl-Ding’s thread wing around the internet that Friday night, told me. Feigl-Ding deleted the SARS tweet once he realized the mistake.