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Effectiveness of COCOA, a COVID-19 contact notification application, in Japan

Kurita, J.; Sugawara, T.; Ohkusa, Y.

2020-07-14 epidemiology
10.1101/2020.07.11.20151597 medRxiv
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BackgroundCOCOA, a contact reporting application in Japan, was launched at the end of June 2020. ObjectWe assessed effectiveness of COCOA. MethodAfter developing a simple susceptible-infected-recovery model with COCOA and voluntary restrictions against going out (VRG), we assumed that COCOA can reduce infectiousness by 10-50% points through self-quarantine at home after receiving notification from COCOA. ResultsCOCOA alone is insufficient to halt an outbreak. Even if the entire population were to use COCOA, the reproduction number would be 1.31. However, if VRG were 15%, about half of the maximum VRG effectiveness under the emergency state declaration, then 10% COCOA use by a population can reduce the reproduction number to less than one. ConclusionSignificant effects of COCOA for reducing the reproduction number were found. However, without VRG, COCOA alone is insufficient to control an outbreak.

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