The Tokyo Foundation for Policy Research


The Tokyo Foundation for Policy Research



New Approach to Inferring the Timing of COVID Infection to Mitigate the Spread of New Variants

Multiple waves of COVID-19 outbreaks have been caused by the emergence and importation of new variants. To prevent the importation of new variants, a combination of border control and contact tracing is essential, but the timing of infection inferred by interviews can be influenced by recall bias, hindering the contact tracing process.

Senior Fellow Keisuke Ejima, Research Director Kenji Shibuya, and other researchers have published a paper in BMC Infectious Diseases proposing a novel approach to infer the timing of infection by employing a within-host model to capture viral load dynamics after the onset of symptoms.

Analyzing the 12 initial reported cases in Singapore—considered imported because of travel history to Wuhan—the researchers applied this approach to ascertain secondary transmission. Contact tracing combined with this approach could be the key to mitigating the risk of importation of new variants by identifying cases as early as possible and inferring the timing of infection with high accuracy.

“Estimation of timing of infection from longitudinal SARS-CoV-2 viral load data: Mathematical modelling study,” BMC Infectious Diseases

Profile of Senior Fellow Keisuke Ejima

Profile of Research Director Kenji Shibuya



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