Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus

High Number of Undocumented Infections Supported Rapid Spread of COVID-19 Outbreak in China

In China, undocumented cases of the novel coronavirus were quite numerous before travel restrictions were put in place in late January 2020, and these undetected infections contributed to the majority of virus spread. These findings, based on a modeling study, explain the rapid geographic spread of SARS-CoV2 in China, the study’s authors say. Estimation of the prevalence and contagiousness of undocumented SARS-CoV2 infections is critical for understanding the overall pandemic potential of the COVID-19 disease, particularly as undocumented infections can expose a far greater portion of the population to the virus than would otherwise occur.

To better understand the fraction of undocumented infections that contributed to China’s outbreak, Ruiyun Li and colleagues developed a mathematical modeling approach that combined data on people’s movements with reported infection data. They also applied statistical inference techniques. Prior to the 23 January 2020 travel restrictions introduced in Wuhan, 86% of cases of the COVID-19 disease were undocumented, the authors say, a finding that has been independently corroborated. What’s more, these undocumented infections were 55% as contagious as documented infections, the authors say.

The results reveal how government control efforts and population awareness after January 2020 greatly reduced virus transmission, though whether that will continue once control measures are relaxed is unclear, say the authors. The authors note that the key findings of their study “could shift in other countries with different control, surveillance and reporting practices.” They advocate for “a radical increase” in the identification of currently undocumented infections, “to fully control SARS-CoV2.”

NOTE: Today’s noon U.S. E.T. teleconference will also highlight a Science paper by Matteo Chinazzi and colleagues published 6 March, a summary for which is below.

Greatest Benefit to Mitigating the COVID-19 Epidemic Will Come from Public Health Interventions and Behavioral Changes

In areas affected by the 2019 novel coronavirus (COVID-19), travel restrictions will only modestly impact the spread of the outbreak, according to a new modeling study, which estimates the impacts of COVID-19’s spread in and beyond China after establishment of the major quarantine in the Chinese city of Wuhan. Based on the study’s results, the authors say the greatest benefit to mitigating the epidemic will come from public health interventions and behavioral changes that achieve a considerable reduction in the disease transmissibility – factors like early detection, isolation, and handwashing. Their results will inform scientists, public health personnel and policymakers involved in the global response to the epidemic. As the SARS-CoV-2 is expanding out of China, quarantine measures have been enforced from the city of origin – Wuhan in Hubei province – to Cremona in Italy. To understand the impacts of these measures on the dynamics of COVID-19 spread, Matteo Chinazzi and colleagues used a global disease transmission model known as “GLEAM.”

Their results show that the travel ban introduced in Wuhan on January 23, 2020 delayed progression of the epidemic throughout Mainland China by three to five days – a modest effect. When airlines halted flights to and from China starting in early February, this restriction initially helped to slow spread of COVID-19 elsewhere in the world. Though, even in the case of 90% travel reductions, the number of imported cases in other countries went up significantly in a matter of weeks from cases that originated elsewhere, if transmissibility was not reduced through efforts like self-isolation, the authors say. They note that even in the presence of the strong travel restrictions in place to and from Mainland China since January 23, 2020, a large number of individuals exposed to the virus had been traveling internationally without being detected. “Moving forward we expect that travel restrictions to COVID-19 affected areas will have modest effects, and that transmission-reduction interventions will provide the greatest benefit to mitigate the epidemic,” they say.

Original research article:

DOI: 10.1126/science.abb3221

Images: and Food and Drug Administration

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