Study: Undocumented COVID-19 Cases Fueled Rapid Disease Spread in China


New research from Columbia University showed undocumented cases of COVID-19 were responsible for over two-thirds of documented infections in China.


New research from Columbia University suggests that undocumented cases of coronavirus disease 2019 (COVID-19) were largely responsible for the rapid spread of the ongoing pandemic.

The results-published online on March 16, 2020 in the journal Science-were based on an advanced computer model of the outbreak within China and found that undocumented COVID-19 cases were responsible for over two-thirds of documented infections.

“Depending on their contagiousness and numbers, undetected cases can expose a far greater portion of the population to virus than would otherwise occur,” said co-author Jeffrey Shaman, PhD, professor of environmental health sciences, Columbia University Mailman School of Public Health, in a university press release. “We find for COVID-19 in China these undetected infected individuals are numerous and contagious. These stealth transmissions will continue to present a major challenge to the containment of this outbreak going forward.”

Shaman and colleagues aimed to assess the full epidemic potential of COVID-19 in China during the weeks before and after the January 23, 2020 travel shutdown in and out of Wuhan, the city at the center of the outbreak.

Using a computer model based on observations of reported infection and spread within China along with mobility data from January 10-23 and January 24-February 8, researchers found:

  • 86% of all infections were undocumented before the travel shutdown

  • Per person, the undocumented cases were half (55%) as contagious as documented cases, but were the source of 79% of documented cases

“Heightened awareness of the outbreak, increased use of personal protective measures, and travel restriction have helped reduce the overall force of infection; however, it is unclear whether this reduction will be sufficient to fully stem the virus spread,” said Shaman in the press release. “If the novel coronavirus follows the pattern of 2009 H1N1 pandemic influenza, it will also spread globally and become a fifth endemic coronavirus within the human population.”

The authors cautioned that these findings could shift in other countries depending on the control, surveillance, and reporting practices put in place.

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