Research Article

Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing

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Science  08 May 2020:
Vol. 368, Issue 6491, eabb6936
DOI: 10.1126/science.abb6936

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  • Body temperature recoding in the digital contact tracing app to COVID-19
    • Shu Yuan, Professor, College of Resources, Sichuan Agricultural University
    • Other Contributors:
      • Si-Cong Jiang, Researcher, Chengdu KangHong Pharmaceutical Group Comp. Ltd.
      • Zi-Lin Li, Surgeon, Department of Cardiovascular Surgery, Xijing Hospital, Medical University of the Air Force

    Ferretti et al. (1) explored the feasibility of protecting the population by questionnaires versus algorithmic instantaneous coronavirus disease 2019 (COVID-19) contact tracing assisted by a mobile phone application. This tracing method may be great helpful to discriminate susceptible population, however some convenient and pre-diagnostic method specific to mild/asymptomatic patients still need to be developed urgently, since the close contacts without symptoms do not always take the viral nucleic acid test.
    Clinical studies in China and USA found that the average body temperature of the patients on admission was 37.3°C (2, 3), and the average maximum temperature during hospitalization was 38.3°C (2), which were 0.5°C and 1.5°C higher than the normal body temperature of 36.8°C respectively. Therefore, body temperature is a good indicator for the viral infection (either symptomatic or asymptomatic). At least a rise of 0.5°C would be a diagnostic criteria. However, many patients' basal body temperatures are below 36.8°C (4), and a rise of 0.5°C would not be defined as a fever case, resulting in missed diagnosis.
    The individual's body temperature changes significantly within a day (<1.0°C), influenced by diet, exercise state, mental factors and so on (5). A rise of 0.5°C could not be discriminated accurately. In order to reflect the changing trend more accurately, we propose a method of rolling monitoring body temperatures: recording axillary temperat...

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    Competing Interests: None declared.
  • COVID-19 epidemic control by ethical artificial intelligence
    • Yuichi Hirata, Associate Professor, Hokkaido University, Central Institute of Isotope Science, Graduate School of Biomedical Science and Engineering

    As claimed in (1), in order to control COVID-19 epidemic, a contact-tracing App which builds a memory of proximity contacts and immediately notifies contacts of positive cases shall be utilized only when the ethical requirements for the interventions of such kind are fulfilled to be justified to protect public health.

    For example, the ethical artificial intelligence can be defined to be such contact-tracing App which satisfies such ethical requirements which apply to the use of the App itself and of the data gathered, and commands well-founded public trust and confidence.

    By utilizing digital measures developed by the faster digitalized big science (2), such ethical artificial intelligence shall perform ethical behaviors for ensuring safety and health of the residents of local areas.

    In such situations, the ethical artificial intelligence shall play roles for human health as computer software algorithms for performing tasks for which a human ethical brain is normally considered necessary.

    Such ethical artificial intelligence shall promptly be implemented in infrastructures of the local areas to provide real time information of health conditions of local residents and their moving and infection paths and health care facilities and available medical treatments, and shall perform adaptive and optimized control of the residents flow to perform appropriate comprehensive ethical risk management of COVID-19 and reduce its ethical risks to prevent COVID...

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    Competing Interests: None declared.
  • A caution on the use of smartphones for contact tracing
    • William Waites, Postdoctoral Researcher, School of Informatics, University of Edinburgh

    Dear Dr Ferretti et al.,

    Though App-assisted contact tracing would indeed address some of the difficulties in terms of speed and volume with the manual method, it is important to recognise the limitations of this approach. In particular, it seems likely that it will not be possible to achieve sufficient uptake with voluntary, privacy-preserving techniques as have been proposed for this to be more than an adjunct to traditional methods. Furthermore, uptake is likely to be lower in more vulnerable communities which risks a social divide.

    Hellewell et al. (6) examine the success rate of contact tracing required for control of an outbreak. According to their model, given a basic reproduction number of 2·5, upwards of 80% of contacts must be traced in order to reduce the effective reproduction number below the critical threshold. In the presence of asymptomatic or presymptomatic transmission, the required success rate of contact tracing increases rapidly. They conclude that contact tracing alone will be insufficient to control future outbreaks.

    It is possible to ask what the maximum success rate we can expect from smartphone apps is, to judge how realistic it would be to try to achieve the success rate that Hellewell et al. suggest would be needed. There are important technical limitations that prevent participation. Unmodified smartphone operating systems do not allow apps to use beacon functionality unless they remain open. This has a deleterious effect o...

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    Competing Interests: None declared.
  • Could the control of the SARS-CoV-2 epidemic be achieved by digital contact tracking alone?
    • Victor Santana Santos, Head of the Centre for Epidemiology and Public Health., Federal University of Alagoas, Brazil.
    • Other Contributors:
      • Paulo Ricardo Martins-Filho, Head of the Investigative Pathology Laboratory., Federal University of Sergipe, Brazil.

    With interest, we read the study conducted by Ferretti et al (1). Their manuscript showed that viral spread is too fast to be contained by manual contact tracing, and a contact-tracing App could be faster, more efficient and happened at scale. However, some concerns about the wide use of App can be raised. As the COVID-19 pandemic has spread rapidly to more fragile communities (2), the systematic and extensive use of the App could be impacted by the limited access to the internet, as an estimated 2 billion people live in a country where 1GB of data costs over 5% of what people earn in a month (3). Moreover, for millions of people living in highly dense communities following the main recommendations to control the dissemination of COVID-19 – social distancing and frequent handwashing – are not easy (4).
    In addition, the App recommended by the authors can benefit if it is accompanied by a steadfast contact tracing strategy, where the collected samples are easily and quickly processed, allowing speed in the availability of results. Currently, the main diagnostic method of COVID-19 is based on amplification of nucleic acids which need well-trained laboratory technicians and they are often performed in centralized laboratories, which can delay the results. An alternative would be the use of the App plus a strategy using the tracking of contacts by point-of-care tests. However, the World Health Organization does not currently recommend the use of antigen-detecting rapid di...

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    Competing Interests: None declared.
  • Assumptions about app adoption?

    In your interactive dashboard at, shouldn't there be a parameter for differing assumptions about percentage app adoption in a population? Can you be more explicit about how you've addressed this critical variable?

    Competing Interests: None declared.
  • RE: Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing
    • Haolong Hou, MBA, Bioinformatics Researcher, Web Developer, Drexel University

    Dear Professor Christophe Fraser,

    Thank you for your meaningful work on proving the effectiveness of mobile app tracing!

    Since the Lunar New Year’s Eve, I have also been working on such a novel but simple solution to help control the COVID-19 pandemic. I call it #ABCvirusRadar. It is a fully digital attempt based on smartphone devices and has been released for public use since February. I have written a short article introducing my work here: A Digital Solution Helps Control the Pandemic - #ABCvirusRADAR

    I have read your paper with my limited knowledge in epidemiology area. There are a possible flaw in your assumption and several important typos caught my attention as listed below.
    1. On Supplementary Page 4, the second assumption for equation 13 assumed that Beta_pre-sym = Beta_sym. However, according to my research (, Question 2. How are COVID-19 and influenza viruses different? Answer Paragraph 2), the two Betas should not be assumed equal (“while we are learning that there are people who can shed COVID-19 virus 24-48 hours prior to symptom onset, at present, this do...

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    Competing Interests: I have developed and released (on Feb. 8th) a mobile miniApp named #ABCvirusRADAR, which is the same or highly similar to the one described in this paper. Also, I am working on an article discussing the methodology and application of the #ABCvirusRADAR app and the framework as a whole solution for combating the COVID-19 pandemic. A computer simulation approach, which could be an addition to this paper, will also be introduced.
  • RE: Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing

    One significant ethical consideration needs to be addressed specifically. That is, who will have control of the app and of the data it gathers. The app should be under the users' control, this means it must be free software. Data should not be stored by a single entity, it should work using a distributed network. Perhaps something similar to blockchain technology or peer-to-peer sharing.

    The Ethical Considerations section does mention "The use of a transparent and auditable algorithm" but this is very vague. It doesn't explain who will be able to audit the algorithm or how much of the app constitutes "the algorithm". Free software is the only ethical manner in which a government can request its citizens to use an app (compulsory or not).

    Competing Interests: None declared.

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