March 25, 2020

Undocumented COVID-19 Infections and Transmission — Hidden Disaster

Hana M. El Sahly, MD reviewing Li R et al. Science 2020 Mar 16

In China, undocumented infections fueled the rapid early spread of SARS-CoV-2.

The proportion of individuals infected with SARS-CoV-2 who have minimal symptoms is an important determinant of the pathogen's pandemic potential, as these infections are likely to go undiagnosed. Investigators used mathematical modeling to estimate the number of undocumented infections and their contribution to SARS-CoV-2 transmission in China.

Subjects were categorized into two groups: those with symptoms severe enough to elicit care-seeking and a documented COVID-19 diagnosis, and those with undocumented infections. The model also accounted for changes in human mobility between cities based on recent historic data adjusted for the escalating restrictions on such movement.

At the beginning of the epidemic, the estimated basic reproductive number (R0) was 2.38 and the percentage of undocumented infections was 86.0%. Undocumented infections were estimated to cause 86.2% of all infections. Later in the epidemic and with augmented testing, the proportion of undocumented infections fell to 35%, and the R0 dropped to 1.36 and then to 0.99 as restrictions on geographic movement tightened.

COMMENT

To end an epidemic, R0 must be kept below 1.0 in a sustained fashion. Mathematical modeling of epidemics is fraught with uncertainty given its reliance on numerous assumptions that sometimes turn out to be faulty. However, this study's rigorous modeling data underscore that drastic, prolonged geographic mobility restrictions are needed to contain the SARS-CoV-2 pandemic. Many countries are currently paying this high societal cost while awaiting the advent of an effective vaccine.

EDITOR DISCLOSURES AT TIME OF PUBLICATION

Disclosures for Hana M. El Sahly, MD at time of publication

Consultant/Advisory Board	Emmes Corp.
Grant/Research Support	NIH

CITATION(S):

Li R et al. Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2). Science 2020 Mar 16; [e-pub]. (https://doi.org/10.1126/science.abb3221)