key: cord-0835960-ves3pzl4 authors: Kurita, Junko; Sugawara, Tamie; Ohkusa, Yasushi title: Effect of emergency declaration for the COVID −19 outbreak in Tokyo, Japan in the first two weeks date: 2020-04-21 journal: nan DOI: 10.1101/2020.04.16.20067447 sha: 62f2604d25827246d53666601b9bd90e346530a4 doc_id: 835960 cord_uid: ves3pzl4 Background: Prime Minister of Japan Abe declared an emergency to control the COVID−19 outbreak on April 7, 2020. He asked almost half of the population of Japan to reduce their personal contacts by 70−80%. Object: This study estimates the effectiveness of that emergency declaration. Method: We applied a simple susceptible−infected−recovery model to data of patients with symptoms in Tokyo, Japan for January 14 − April 21 as of April 22. We estimate the reproduction number in four periods: R0 before voluntary event cancellation and school closure (VECSC) which was introduced since February 27 to March 19, Rv during the VECSC, Ra after VECSC, and Re after the emergency declaration. Results: Results suggest that the value of R0 was estimated as 1.267; its range was [1.214, 1.341]. However, Rv was estimated as 2.360 [1.844, 2.623]. Ra was estimated as 2.307 [2.035, 2.794] and Re was 0.462 [0.347, 0.514]. Discussion and Concussion: One must be reminded that these results reflect only those at two weeks after the emergency declaration. The reproduction number probably changed thereafter continuously. To control the COVID-19 outbreak in Japan, the Prime Minister Abe declared an emergency on April 7 and applied countermeasures starting from April 8 [1] . The declared measures required residents of seven prefectures, collectively accounting for 44.5% of Japan's population, to restrict their trips outside the home voluntarily. Voluntary compliance means that the declared measures were not enforced as law. People were not arrested even if they do not comply with this government declaration. At the same time, the policy required the reduction of contact by 70-80%, based on the author's earlier research [2] . However, the share of the population cooperating with government requirements without law enforcement has remained uncertain. Therefore, this policy's effects must be evaluated as nearly and in as real-time a manner as possible. If the reproduction number after the emergency declaration (R e ) is less than one, then the government would be able to rescind the declaration earlier. If greater than one, and especially of greater than two, then a more powerful policy, including law enforcement, might be necessary. Therefore, we undertook preliminary evaluation of the effect as of April 14, at one week after the declaration was issued. Method All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Onset dates were sometimes unreported. Therefore, we estimated the onset date. To do so, we inferred a distribution of the length from onset to reporting based on patients for whom onset dates were available. Then we applied this empirical distribution to patients for whom onset dates were not available. Letting f(k) represent this empirical distribution and letting Nt denote the number of patients for whom onset dates were not available published at date t, then the number of patients for whom the onset date was All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 21, 2020. . https://doi.org/10.1101/2020.04.16.20067447 doi: medRxiv preprint t-1. The number of patients for whom onset dates were not available was estimated as f(1)Nt. Similarly, the number of patients with onset date t-2 and whose onset dates were not available was estimated as f(2)Nt. Therefore, the total number of patients whose onset date were not available, given an onset date of s, was estimated as Σ k=1 f(k)Ns+k for a long time passed from s. Moreover, the reporting delay for published data from MHLW might be considerable. In other words, if s+k was larger than that in the current period t, then s+k represents the future for period t: thus Ns+k was not observable. Such a reporting delay causes an under-estimation bias in the number of patients. Therefore, we must adjust it as Σ k=1 t-s Similarly, patients for whom the onset dates were available are expected to be affected by the reporting delay. Thus we have Ms|t /Σ k=1 Ms|t represents the reported number of patients for whom onset dates were within period s extending until the current period t. We applied a simple susceptible-infected-recovery (SIR) model [2] [3] [4] to the epidemic curve for Japan, with 120 million populations. We assume an incubation period calculated according to the empirical distribution. Symptomatic and asymptomatic states continued for one week and then moved to a recovery state with probability of one. We are not concerned about outcomes or All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 21, 2020. . https://doi.org/10.1101/2020.04.16.20067447 doi: medRxiv preprint necessary medical resources in this model. Therefore, the state of death or hospitalization was not incorporated into the model. Asymptomatic cases cannot be observable unless complete laboratory-based surveillance is performed. One exceptional study found the asymptomatic cases to be 3/23 among elderly people [5] . For these analyses, the powers of infectivity among severe patients and mild patients were equal. Moreover, we assumed that asymptomatic cases have the same power of infectivity as symptomatic cases have [5] . The distribution of infectiousness in symptomatic and asymptomatic cases was assumed to be 30% on the onset day, 20% the following day, and 10% for the next five days [5] . We sought R 0 , R v, R a , and R e .to fit the data to minimize the sum of absolute values of discrepancies among the bootstrapped epidemic curve and the fitted values. The estimated distribution of three reproduction numbers was calculated using 10,000 iterations of bootstrapping from the empirical distribution of the data obtained for symptomatic patients. We estimated the results sequentially as follows: We first estimated R 0 as the best fit to bootstrapped data in the pre-VECSC period. Then based on the obtained R 0 and course of the outbreak in the pre-VECSC period, we estimated R v as the best fit to bootstrapped data for the VECSC period. Similarly, based on the obtained R 0 and R v , All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 21, 2020. . https://doi.org/10.1101/2020.04.16.20067447 doi: medRxiv preprint we estimated R a as the best fit to bootstrapped data in the post-VECSC period. Finally, based on the obtained R 0 , R v , and R a , we estimated R e as the best fit to a bootstrapped data after the emergency was declared. For each step, reproduction numbers were grid-searched in the interval of (0, 10) by 0.001 resolution. Data used were the numbers of symptomatic patients during January 14 -April 13 reported by MLHW [6] as of April 14. During this period, 6084 cases with onset dates were reported. We excluded imported cases and those who were presumed to have been infected passengers and crew from the Diamond Princess: they were presumed not to be community-acquired cases in Japan. Of those, onset dates were available for 3734 cases; onset dates were not reported for other cases. All information used for this study has been published. There is therefore no ethical issue related to this study. All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 21, 2020. . https://doi.org/10.1101/2020.04.16.20067447 doi: medRxiv preprint Figure 1 depicts the empirical distribution among incubation periods of 91 cases for which exposure dates and onset dates were reported by MHLW. Its mode was six days. Its average was 6.6 days. Figure 2 depicts the empirical distribution of duration from onset to report. We adjusted the reporting delay based on this distribution. We applied a simple SIR model to all cases, including asymptomatic cases that had not been incorporated into the model to date. An earlier study [7] [8] [9] [10] estimated R 0 for COVID-19 as 2.24-3.58 in Wuhan. Our R 0 obtained before VECSC was similar. However, an earlier study [11] estimated R 0 in Japan as 0.6 as of the end of February, which was the period mainly before the VECSC was implemented. Such a low number might mislead policy efforts for countermeasures in Japan as it adheres to contact All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Results show a dramatic decrease in the reproduction number on the basis of the emergency declaration. The outbreak will be contained in a few weeks if the success continues at the same level. In other words, the 0.6 figure reported from an earlier study was comparable with our estimation for the period after the emergency declaration, even though no countermeasure was used before VECSC. However, after VECSC, the reproduction number escalated again to become higher than that before VECSC. Therefore, a similar phenomenon might occur several weeks after countermeasures cease. One must be reminded that these results reflect only those at one week after the emergency declaration. The reproduction number probably changed thereafter. Results demonstrated that the reproduction number declined dramatically after the emergency declaration. The reproduction number must be monitored carefully and continuously. We hope that the present study contributes to government decision-making about cessation of the emergency declaration. All rights reserved. No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 21, 2020. . https://doi.org/10.1101/2020.04. 16.20067447 doi: medRxiv preprint This study was based on the authors' opinions. The analyses and results do not reflect any stance or policy of our affiliations. Japan state of emergency to cover Tokyo Forecast of the COVID-19 outbreak, collapse of medical facilities, and lockdown effects in Tokyo Preliminary evaluation of voluntary event cancellation as a countermeasure against the COVID-19 outbreak in Japan as of Real-time estimation and prediction for pandemic A/H1N1(2009) in Japan Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility Japan Ministry of Health, Labour and Welfare Are children less susceptible to COVID-19 ? Preliminary Estimation of the Basic Reproduction Number of Novel Coronavirus (2019-nCoV) in China, From 2019 to 2020: A Data-Driven Analysis in the Early Phase of the Outbreak The reproductive number of COVID-19 is higher compared to SARS coronavirus Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and Coronavirus disease-2019 (COVID-19): The Epidemic and the Challenges MHLW COVID-19 Response Team, Mi Suzuki. Closed environments facilitate secondary transmission of coronavirus disease 2019 (COVID-19) We acknowledge the great efforts of all staff at public health centers, medical institutions, and other facilities who are fighting the spread and destruction associated with COVID-19. All rights reserved. No reuse allowed without permission.(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint this version posted April 21, 2020. . https://doi.org/10.1101/2020.04.16.20067447 doi: medRxiv preprint All rights reserved. No reuse allowed without permission.(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint this version posted April 21, 2020. . https://doi.org/10.1101/2020.04.16.20067447 doi: medRxiv preprint All rights reserved. No reuse allowed without permission.(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint this version posted April 21, 2020. . https://doi.org/10.1101/2020.04.16.20067447 doi: medRxiv preprint All rights reserved. No reuse allowed without permission.(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Notes: Bars indicates the number of patients by incubation period among 59 cases whose exposed date and onset date were published by Ministry of Labour, Health and Welfare, Japan.All rights reserved. No reuse allowed without permission.(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint this version posted April 21, 2020. Note: Bars indicates probability of duration from onset to report base on 657 patients whose onset date was available in Japan. Data source was Ministry of Labour, Health and Welfare, Japan.All rights reserved. No reuse allowed without permission.(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint this version posted April 21, 2020. . https://doi.org/10.1101/2020.04.16.20067447 doi: medRxiv preprint