Contact-tracing and peer pressure: how Japan has controlled coronavirus

What we found at an early stage was that efforts to find cases through testing those who had had contact with patients was not particularly effective. Further investigation revealed that while many patients do not infect anyone, some end up infecting many, thereby forming “clusters” of infected people from a single source. Therefore, in addition to contact tracing, we focused on a retrospective tracking of links between patients and found unrecognised cases surrounding the possible source, thereby identifying clusters. In addition, monitoring of the number of unlinked cases led to an early detection of exponential growth in the number of patients, which enabled the government to provide the public with an effective early warning.