Secondary transmission of SARS-CoV-2 during the first two waves in Japan: Demographic characteristics and overdispersion

Yura K. Ko, Yuki Furuse, Kota Ninomiya, Kanako Otani, Hiroki Akaba, Reiko Miyahara, Tadatsugu Imamura, Takeaki Imamura, Alex R. Cook, Mayuko Saito, Motoi Suzuki, Hitoshi Oshitani

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


Objectives: Super-spreading events caused by overdispersed secondary transmission are crucial in the transmission of COVID-19. However, the exact level of overdispersion, demographics, and other factors associated with secondary transmission remain elusive. In this study, we aimed to elucidate the frequency and patterns of secondary transmission of SARS-CoV-2 in Japan. Methods: We analyzed 16,471 cases between January 2020 and August 2020. We generated the number of secondary cases distribution and estimated the dispersion parameter (k) by fitting the negative binomial distribution in each phase. The frequencies of the secondary transmission were compared by demographic and clinical characteristics, calculating the odds ratio using logistic regression models. Results: We observed that 76.7% of the primary cases did not generate secondary cases with an estimated dispersion parameter k of 0.23. The demographic patterns of primary-secondary cases differed between phases, with 20–69 years being the predominant age group. There were higher proportions of secondary transmissions among older individuals, symptomatic patients, and patients with 2 days or more between onset and confirmation. Conclusions: The study showed the estimation of the frequency of secondary transmission of SARS-CoV-2 and the characteristics of people who generated the secondary transmission.

Original languageEnglish
Pages (from-to)365-373
Number of pages9
JournalInternational Journal of Infectious Diseases
Publication statusPublished - 2022 Mar
Externally publishedYes


  • COVID-19
  • Dispersion parameter
  • Overdispersion
  • Secondary transmission
  • Super-spreading events

ASJC Scopus subject areas

  • Microbiology (medical)
  • Infectious Diseases


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