GeekWire reports:

Computer modeling of the coronavirus outbreak’s course in China, in the weeks before a travel shutdown was imposed on Jan. 23, suggest that 86% of the infections went undocumented.

Those undocumented infections were about half as contagious as the documented cases, but were the source of two-thirds of the documented cases, according to a study published online today by the journal Science.

The findings parallel other research into the role of what’s known as stealth or cryptic transmission in spreading the potentially deadly virus. They also underscore the importance of widespread testing, even if patients aren’t experiencing serious symptoms, particularly during the early phases of transmission.

“More active testing procedures would catch more cases,” Columbia University’s Jeffrey Shaman, a co-author of the study, told reporters today. “How that would be implemented is something that we can debate for quite some time. And obviously this all has to be done under the backdrop of the logistics and costs of implementing lots more tests.”

Shaman and his colleagues tracked reports of infections in China from Jan. 10 to 23, and from Jan. 24 to Feb. 8, and fed those reports along with data about population mobility into their computer model.

When the researchers started putting their data together, they suspected the model would show that reported cases were just “the tip of the iceberg” for the spread of infection, Shaman said. That suspicion was based on past research involving more benign coronaviruses — such as those that cause the common cold. Such research suggested that most infections caused symptoms so mild that the people who had the virus didn’t bother to report them.

Their suspicion turned out to be correct. “It’s the undocumented infections which are driving the spread of the outbreak,” Shaman said. [Continue reading…]