Was Japan's cluster-based approach toward coronavirus disease (COVID-19) a fantasy?

TANAKA Sigeto <http://tsigeto.info>
(Graduate School of Arts and Letters, Tohoku University)

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• Title: Was Japan's cluster-based approach toward coronavirus disease (COVID-19) a fantasy?: Re-examining the clusters' data of January-March 2020
• Author: TANAKA Sigeto || 田中 重人
• Server: Research Square
• Date: 2023-03-17
• Language: ENG
• DOI: 10.21203/rs.3.rs-2647575/v1
• ISSN: 2693-5015

URI: http://tsigeto.info/23g

OSF project: https://osf.io/52nvs

Abstract

BACKGROUND: The Japanese government and experts have claimed that they adopted the “cluster-based” approach to suppress the spread of novel coronavirus disease 2019 (COVID-19) in early 2020 by detecting clusters through the retrospective tracing of infection sources. Moreover, they considered this approach to be a significant contributor in the prevention of outbreaks. However, this claim is not corroborated by existing literature, which consistently described COVID-19 clusters as comprising a relatively small proportion of the total number of cases detected during the period.

METHODS: To determine whether Japan successfully implemented the cluster-based approach in January?March 2020, the author collected publicly available information regarding 25 clusters (groups of five or more COVID-19 cases that came in contact at a common venue) reported by the Ministry of Health, Labour, and Welfare as of March 31, 2020. These clusters were classified into retrospectively or prospectively reached using a tracer. The number of cases related to each cluster was determined.

RESULTS: Among 2135 COVID-19 cases confirmed until the end of March 2020 in Japan, 9.3% of the cases were related to the five clusters found by retrospective tracing. In contrast, 35.3% of the cases were related to the 20 clusters found by prospective tracing, while 55.4% were unrelated to any cluster.

CONCLUSIONS: Japan's COVID-19 response in early 2020 was not cluster based. Retrospective tracing has a limited contribution in detecting infectious cases and preventing further transmissions. The surveillance system mainly detects non-cluster cases and cluster-related cases using prospective contact tracing.

Contents

• Background
  • Japan's “cluster-based approach”
  • Questions
  • The aim of this study
• Methods
• Results
• Discussion
• Abbreviations
• Notes
• References
• Supplementary Files

Table and figure

• Table 1: Overview of the clusters from January to March 2020 in Japan
• Figure 1: Breakdown of the coronavirus disease cases until March 31, 2020 in Japan

Communication

Questions/comments are welcome.

• E-mail
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• OSF project

Related sites and pages

• The Japan Model for COVID-19 Response
• Earlier version: [* The reported number of COVID-19 cases and its interpretion as official statistics: The changing connotation of "cluster"] (Kansai Sociological Association, 73th Conf. (online) 2022-05-29)
• Japanese presentation with updated data: [* Revisiting facts from a few years ago: fictiousness of Japan's “cluster-based approach” toward COVID-19] (Japanese Studies Workshop, 6th Conf. (Sendai), 2025-03-16)
• Revised version: Was Japan's cluster-based approach toward coronavirus disease (COVID-19) a fantasy?: Re-examining the clusters' data of January-March 2020 (Annual Reports of Graduate School of Arts and Letters, Tohoku University, 75:96-83, 2026)

Tohoku Univ / School of Arts and Letters / Innovative Japanese Studies / TANAKA Sigeto

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