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Mathematical Biosciences and Engineering ; 19(12):13137-13151, 2022.
Article in English | Scopus | ID: covidwho-2055536


The basic reproduction number, R0, plays a central role in measuring the transmissibility of an infectious disease, and it thus acts as the fundamental index for planning control strategies. In the present study, we apply a branching process model to meticulously observed contact tracing data from Wakayama Prefecture, Japan, obtained in early 2020 and mid-2021. This allows us to efficiently estimate R0 and the dispersion parameter k of the wild-type COVID-19, as well as the relative transmissibility of the Delta variant and relative transmissibility among fully vaccinated individuals, from a very limited data. R0 for the wild type of COVID-19 is estimated to be 3.78 (95% confidence interval [CI]: 3.72–3.83), with k = 0.236 (95% CI: 0.233–0.240). For the Delta variant, the relative transmissibility to the wild type is estimated to be 1.42 (95% CI: 0.94–1.90), which gives R0 = 5.37 (95% CI: 3.55–7.21). Vaccine effectiveness, determined by the reduction in the number of secondary transmissions among fully vaccinated individuals, is estimated to be 91% (95% CI: 85%–97%). The present study highlights that basic reproduction numbers can be accurately estimated from the distribution of minor outbreak data, and these data can provide further insightful epidemiological estimates including the dispersion parameter and vaccine effectiveness regarding the prevention of transmission. © 2022 the Author(s), licensee AIMS Press.

Public Health ; 187: 157-160, 2020 Oct.
Article in English | MEDLINE | ID: covidwho-733655


OBJECTIVES: The Japanese prime minister declared a state of emergency on April 7 2020 to combat the outbreak of coronavirus disease 2019 (COVID-19). This declaration was unique in the sense that it was essentially driven by the voluntary restraint of the residents. We examined the change of the infection route by investigating contact experiences with COVID-19-positive cases. STUDY DESIGN: This study is a population-level questionnaire-based study using a social networking service (SNS). METHODS: To assess the impact of the declaration, this study used population-level questionnaire data collected from an SNS with 121,375 respondents (between March 27 and May 5) to assess the change in transmission routes over the study period, which was measured by investigating the association between COVID-19-related symptoms and (self-reported) contact with COVID-19-infected individuals. RESULTS: The results of this study show that the declaration prevented infections in the workplace, but increased domestic infections as people stayed at home. However, after April 24, workplace infections started to increase again, driven by the increase in community-acquired infections. CONCLUSIONS: While careful interpretation is necessary because our data are self-reported from voluntary SNS users, these findings indicate the impact of the declaration on the change in transmission routes of COVID-19 over time in Japan.

Coronavirus Infections/prevention & control , Coronavirus Infections/transmission , Disease Outbreaks/prevention & control , Pandemics/prevention & control , Pneumonia, Viral/prevention & control , Pneumonia, Viral/transmission , Adolescent , Adult , Aged , Aged, 80 and over , COVID-19 , Community-Acquired Infections/epidemiology , Contact Tracing , Coronavirus Infections/complications , Coronavirus Infections/epidemiology , Female , Humans , Japan/epidemiology , Male , Middle Aged , Occupational Health/statistics & numerical data , Pneumonia, Viral/complications , Pneumonia, Viral/epidemiology , Self Report , Social Networking , Surveys and Questionnaires , Symptom Assessment , Young Adult