'Stealth transmission' fuelling fast spread of coronavirus outbreak: Study

Undetected novel coronavirus cases, many of which did not show severe symptoms, were largely responsible for the rapid spread of the deadly COVID-19 outbreak in China, according to a study.

The research, published in the journal Science, found that 86 per cent of all coronavirus infections were undocumented prior to the January 23 travel shutdown in Wuhan.

Scientists at Columbia University in the US noted that per person, these undocumented infections were half as contagious as documented ones.

"The explosion of COVID-19 cases in China was largely driven by individuals with mild, limited, or no symptoms who went undetected," said study co-author Jeffrey Shaman, a professor at Columbia University Mailman School.

"Depending on their contagiousness and numbers, undetected cases can expose a far greater portion of the population to virus than would otherwise occur," Shaman said.

The researchers found that 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, they said.

The researchers used a computer model that draws on observations of reported infection and spread within China in conjunction with mobility data from January 10-23 and January 24-February 8.

"Heightened awareness of the outbreak, increased use of personal protective measures, and travel restriction have helped reduce the overall force of infection," said Shaman.

"However, it is unclear whether this reduction will be sufficient to fully stem the virus spread," he said.

"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," Shaman said.