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. 2021 Sep 7;9(4):cnab026. doi: 10.1093/comnet/cnab026

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© The authors 2021. Published by Oxford University Press. All rights reserved.

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Fig. 1. — Human-to-human COVID-19 spread by backward contact tracing. Arrows stem from COVID-19 officially confirmed cases (red circles) to their potential origin of infection (grey circles).