Undocumented cases fuelling fast spread of COVID-19: Study

New York, March 18 (IANS) Researchers have found that undetected cases, many of which were likely not severely symptomatic, were largely responsible for the rapid spread of the novel coronavirus (COVID-19) outbreak in China.

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

Per person, these undocumented infections were half (52 per cent) as contagious as documented infections yet were the source of two-thirds of documented infections, according to the research.

"The explosion of COVID-19 cases in China was largely driven by individuals with mild, limited, or no symptoms who went undetected. Depending on their contagiousness and numbers, undetected cases can expose a far greater portion of the population to virus than would otherwise occur," said study co-author Jeffrey Shaman, Professor at Columbia University in the US.

"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 added.

Government control efforts and population awareness have reduced the rate of spread of the virus in China; after travel restrictions and control measures were imposed, it spread less quickly, the study has revealed.

For the findings, 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.

They cautioned that major changes to care-seeking or patient documentation practices, as well as rapid developments with regard to travel restrictions and control measures, may make predictions difficult.

"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," Shaman 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 added.