key: cord-0255113-sj0mgc86 authors: Yen, A. M.-F.; Chen, T. H.-H.; Chang, W.-J.; Lin, T.-Y.; Jen, G. H.-H.; Hsu, C.-Y.; Wang, S.-T.; Dang, H.; Chen, S. L.-S. title: Epidemic Surveillance Models for Containing the Spread of SARS-CoV-2 Variants: Taiwan Experience date: 2021-10-23 journal: nan DOI: 10.1101/2021.10.19.21265107 sha: a9b29ed446e5bf629e273e851cb6cecd74b7e512 doc_id: 255113 cord_uid: sj0mgc86 Objectives: Two kinds of epidemic surveillance models are presented for containing the spread of SARS-CoV-2 variants so as to avert and stamp out a community-acquired outbreak (CAO) with non-pharmaceutical interventions (NPIs), tests, and vaccination. Design: The surveillance of domestic cluster infections transmitted from imported cases with one-week time lag assessed by the Poisson model and the surveillance of whether, how and when NPIs and test contained the CAO with the SEIR model. Settings: Border and Community of Taiwan. Main Outcome Measurements: The expected number and the upper bound of the 95% credible interval (CrI) of weekly covid-19 cases compared with the observed number for assessing the threshold of a CAO; effective reproductive number (Rt) and the effectiveness of NPIs for containing a CAO. Results: For the period of January-September 2020 when the wild type and the D614G period were prevailing, an increase in one imported case prior to one week would lead to 9.54% (95% CrI 6.44% to 12.59%) higher risk of domestic cluster infection that provides a one-week prior alert signal for more stringent NPIs and active testing locally. Accordingly, there was an absence of CAO until the Alpha VOC period of February 2021. However, given level one of NPI alert the risk of domestic cluster infections was gradually elevated to 14.14% (95% CrI 5.41% to 25.10%), leading to the Alpha VOC CAOs of six hotspots around mid-May 2021. It took two-and-half months for containing this CAO mainly with level three of NPI alert and rapid test and partially by the rolling out of vaccination. By applying the SEIR model, the Rt decreased from 4.0 at beginning to 0.7 on 31 July 2021 in parallel with the escalating NPIs from 30% to 90%. Containing a small outbreak of Delta VOC during this CAO period was also evaluated and demonstrated. After controlling the CAO, it again returned to imported-domestic transmission for Delta VOC from July until September 2021, giving an estimate of 10.16% (95% CrI: 7.01% to 13.59%) for the risk of several small cluster infections. However, there was an absence of CAO that resulted from the effectiveness of NPIs and tests, and the rapid expansion of vaccination. Conclusions: Averting and containing CAOs of SARS-CoV-2 variants are demonstrated by two kinds of epidemic surveillance models that have been applied to Taiwan scenario. These two models can be accommodated to monitor the epidemic of forthcoming emerging SARS-CoV-2 VOCs with various circumstances of vaccine coverage, NPIs, and tests in countries worldwide. As of September 2021, many countries around the world have experienced repeated surges of covid-19 epidemic alternating between lifting and operating nonpharmaceutical interventions (NPIs) in the facing of lasting covid-19 pandemic before and after the era of vaccination. [1] [2] [3] [4] It should be noted that such a transmission is also aggravated by the emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants, particularly Variants of Concerns (VOCs) and Variants of Interests (VOIs) that not only increase transmissibility, leading to the rapid spread from importation, household, institution, and community, but also have a higher likelihood of escaping immune response after vaccination, resulting in vaccine breakthrough. [4] [5] [6] [7] It is customary to see a series of repeated surges of community-acquired outbreaks (CAOs) often resulting from the spread of the imported cases of each country while quarantine and isolation of the border control are ineffective. Largescale community covid-19 outbreaks were noted in many countries after the first wave of imported case 2, 8, 9 and the subsequent global spread through inter-continental transmission even after border control measures and travel restriction operated by many countries. 2, [8] [9] [10] [11] [12] [13] [14] It is well recognized that the transmission routes lead to largescale CAOs often begin with small cluster infections among households and institutions due to careless quarantine and isolation of importation cases that render . CC-BY-NC 4.0 International license It is made available under a perpetuity. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021. 10.19.21265107 doi: medRxiv preprint susceptibles become infected after close contact with them. In the absence of NPIs on population level, these infectives resulting from small cluster infections may be further propagated into a large epidemic episode in the neighborhood of community and were further spread into hotspot over hotspot. 9, 13, 15 This can be also observed in recent cluster infections among households and institutions aftermath of vaccine breakthrough. 6, [16] [17] [18] Once CAOs occur after the introduction of importation cases leading to small cluster infections on household and institution level, the transmission route and the mitigating strategy are complicated and would be extended from household, institution, until population level. Monitoring and evaluating the spread of covid-19 epidemic may require the population-based model such as the susceptible-exposedinfected-removal (SEIR) model that evaluate the kinetics of susceptible, infectives, recovery, and death with and without NPIs. Such a transmission route before and after large-scale CAOs would affect the surveillance model for containing the outbreak caused by SARS-CoV-2. There are two epidemic surveillance modes for monitoring the control of an epidemic in the absence and the presence of CAO. The former can be seen in a few countries such as Taiwan and New Zealand where there has been a lack of large-scale covid-19 CAOs for a long period before 2021 because of the strict operation of NPIs is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021. 10.19.21265107 doi: medRxiv preprint including early boarder quarantine, symptom-based screening, contact tracing, isolation, wearing masks in crowded settings, and social distancing. 19, 20 As the epidemic surveillance model for monitoring imported cases to reduce the chance of cluster infections resulting in domestic cases would be different from that for assessing the spread of a CAO. Very few studies were conducted to provide various epidemic surveillance models in the presence and the absence of CAO during covid-19 pandemic in parallel with the evolution of SARS-CoV-2 variants. The Taiwan covid-19 surveillance model is proposed here to demonstrate how to avert and contain covid-19 epidemics evolving with SARS-CoV-2 variants from January 2020 to August 2021, which is further divided into two phases, the non-VOC is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021. 10.19.21265107 doi: medRxiv preprint evaluate whether, how, and when NPIs and vaccine, if available, can end each episode of community-acquired infection. Stemming from the coping strategies of NPIs, testing, and vaccination, the aim of this study is to present two epidemic surveillance models for monitoring and containing the spread of covid-19 caused by SARS-CoV-2 variants during the periods without and with CAOs. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The publicly available information on covid-19 including the daily number of cases, recovered, and deaths from 1 January 2020 to 31 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021. 10.19.21265107 doi: medRxiv preprint The containment measures of the non-VOC phase in Taiwan centered on two strategies, namely border control and quarantine and isolation. They are detailed as follows. The first confirmed covid-19 case in Taiwan developed symptoms on 11 January 2020 in Wuhan and traveled to Taiwan on 21 January 2020. This imported case was quarantined at airport and later confirmed by using reverse transcription polymerase chain reaction (RT-PCR) test. Four imported cases were confirmed afterwards before the first domestic case was confirmed on 28 January 2020, who is the family contact of a previously imported case. In response to the risk of CAO caused by the imported-domestic transmission, Taiwanese government issued a provisional regulation for border control to ban the flights from mainland China and Hong-Kong on 7 February 2020. Following the implementation of this border control regulation, there were sparse imported and domestic cases up to 5 March 2020. Supplementary figure 1 shows the timelines regarding the evolution of implemented border control measures for this non-VOC phase. There was a surge of imported cases resulting mainly from the Taiwanese returning from high risk areas abroad in mid-March, followed by an increase in domestic cases in the subsequent weeks. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint Following the guideline announced by Taiwan CECC, subjects with classical covid-19 symptoms including fever, cough, short of breath, fatigue, myalgia, diarrhea, and newly onset agnosia would be tested for SARS-CoV-2 infection with RT-PCR. For subjects with the history of the contact with suspected cases, it is mandatory for these subjects to be under quarantine for 14 days. The quarantined subjects were tested for SARS-CoV-2 upon the occurrence of suspected symptoms during their 14day quarantine period. As a supplementary measure for border control, a 14-day quarantine period is mandatory for all passengers travel to Taiwan since 19 March 2020 (14-day quarantine policy, supplementary figure 1). Subjects with classical symptoms will be tested with RT-PCR for identifying covid-19 cases during the quarantine period. The policy of testing was augmented by the requirement of a negative RT-PCT before boarding and at the end of the 14-day quarantine period since 1 December 2020. The covid-19 cases in Taiwan in year 2020 were mainly comprised of imported cases (fig 1) . The risk of CAO following the transmission of covid-19 to community caused by these imported cases were largely diminished by the border control strategies and quarantine and isolation in conjunction with NPIs such as wearing mask and social distancing. 20, 23 Supplementary is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint figure 1 ). 24, 25 In addition to the implementation of strict NPIs by scaling up to level three alert, community-based active surveillance with rapid test stations were utilized for the identification of covid-19 cases at earliest to block the transmission in community. We used a Bayesian random-effects Poisson regression model 26 to calculate the expected weekly domestic infected cases following the imported cases of covid-19. The Poisson model has been widely applied to the count data on sparse cases, which occurred independently without the possibility of cluster infection. If the predicted . CC-BY-NC 4.0 International license It is made available under a perpetuity. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021.10.19.21265107 doi: medRxiv preprint concurrent-week model (260.3) and two-week lag model (279.5) for imported cases. We used the upper limit of 95% CrI generated by the parameters updated by the data on the non-VOC phase in Taiwan as the threshold for assessing whether cluster infections following imported cases resulted in an emerging CAO. We also used this threshold for alerting the possibility of yielding a large-scale CAO through the imported-domestic transmission in the subsequent week. The possibility of CAO was deemed low if observed domestic cases were not more than the upper limit of the 95% CrI. Otherwise, a CAO was likely to occur and therefore would warrant the implementation of relevant containment measures to prevent a community outbreak. Regarding the impact of imported cases on the occurrence of domestic cases for the Alpha (11 October 2020 to 12 May 2021) and Delta (8 August to 18 September 2021) VOC phase without CAOs in Taiwan, a Bayesian Negative Binomial regression model was applied to taking into account the cluster effect associated with the transmission of covid-19. Following the approach applied for the wild type and D614G period, the one-week lag model was adopted. The estimated results on the risk of imported-domestic transmission and the upper limit of the 95% CrI of expected domestic cases were used for the surveillance of covid-19 in the wake of the second wave of covid-19 pandemic in October 2020 and the Delta VOC period following the stamping out of CAOs during May to July 2021 in Taiwan. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The CAOs in the VOC phase in Taiwan were characterized by using the overall and area-specific incidence between 1 May and 31 July 2021. The data used for analysis consisted of covid-19 cases reported by TCDC during this period. 21 The areaspecific incidence of covid-19 was calculated by dividing the total number of daily cases of each county and city by the population at risk in each area. For a better presentation of the trend of covid-19 incidence, a moving average with a three-day window was applied to avoid the influence of daily fluctuations. By comparing the trend of covid-19 incidences between areas, the effect of containment measures with and without a mass screening campaign were assessed. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021.10.19.21265107 doi: medRxiv preprint recovered were assumed time-invariant, a time-varying transmission coefficient during the period of outbreak captures the change of covid-19 transmission in community affected by the implementation of NPIs and testing. The value of 0.2 and 0.14 were adopted for the two time-invariant rates, σ and α, respectively, by using the information reported in previous studies. 28, 29 The effectiveness of the containment measures for the VOC phase can thus be estimated by where β0 and βt represents the estimated results on the transmission coefficient at initial period and the t th epoch since the occurrence of CAOs in May 2021 in Taiwan. The effective reproductive number, Rt, can then be derived from the estimated results on the time-varying transmission coefficient, βt. To validate the proposed surveillance model for the transmission model from imported to domestic cases during the non-VOC period in Taiwan is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. Patients were not included in the design or conduct of this study. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint Table 1 shows the details of the estimated results of the parameters encoded in the Poisson regression model with a one-week lag of imported cases regarding the three periods without CAO in Taiwan, namely the wild type and D614G period, Alpha VOC period, and Delta VOC period. The upper bound of 95% CrI of those expected cases (dotted line, fig 2) is plotted on the basis of the Poisson regression model in order to provide the threshold of a cluster infection in community caused by the transmission from imported cases one week before. This one-week prior alert on the risk of elevated imported-domestic transmission raises the vigilance on NPIs for averting further CAOs. During the wild type/D614G period, the estimated results based on the Poisson is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint community-acquired cases) in five clusters in Taiwan, including three household clusters (with five, three, and six covid-19 cases, respectively), a medical institute cluster (with nine covid-19 cases), and one academic institute cluster (with four covid-19 cases). Learning from this early period of the wild type of covid-19 provides a strong rationale for being on alert for the ensuing cluster infections preceding one week when imported cases were introduced. This accounted for why none of these five cluster events led to any large-scale CAO in Taiwan because of the advocacy of strict NPIs through CECC. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021.10.19.21265107 doi: medRxiv preprint bound of 95% CrI for the expected domestic cases (20 cases) and the expected domestic cases at weekly basis, the observed domestic cases were kept lower than the upper limit of 95% CrI to avoid large-scale CAOs in April. Since then, there has not been any domestic case until December 2020. There has been no CAO during early Alpha VOC phase of covid-19 pandemic is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. Characteristics of epidemic curves after this CAO are described as follows. There was a CAO emerging from Wanhua, one of the districts with a lower socioeconomic status in Taipei is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021.10.19.21265107 doi: medRxiv preprint cases for this CAO and the subsequent episodes. Fig 3 (a) and (b) show the epidemic curve and the corresponding incidence trend of covid-19 in Taiwan from outbreak until subsidization. It took around two and half months after scaling up level two to nationwide level three of NPIs together with community-based active surveillance of rapid test stations beginning from mid-May. Notably, Fig 3 (b) shows the time trend of covid-19 incidence in Taiwan associated with the implementation of communitybased active surveillance of rapid test stations. By using the active surveillance of the hotspots and its neighborhood, the covid-19 cases, with or without clinical symptoms, can be identified at earliest. The peaks of incidence trend corresponding to the setting of rapid test stations revealed this effect. Supplementary figure 3 shows the incidence trends of six hotspots from the orifice of the emerging outbreak at Taipei with highest incidence to the second wave of outbreaks with lower incidence. The latter may be reduced by the introduction of level three alert of NPI after mid-May. Based on these findings, county-specific incidence rates in Taiwan can be categorized into high, medium, and low areas during CAOs. In addition to the transmission of covid-19 in the community, the high incidence areas were mainly because of early detection of covid-19 cases after transmission via several community-based active surveillance of rapid test stations including three earlier hotspots such as Taipei, New Taipei City, and Miaoli county. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint During the VOC phase of covid-19 outbreak in Taiwan is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint Taiwan, fig 4) , the expected number of cases and epidemic curve caused by Delta VOC without the implementation of enhanced containment measures were projected (supplementary figure 5 (b) ). Had there been no effective containment measures, a total of 75 cases would be expected, which gives the estimated results on effectiveness of NPIs and testing in reducing covid-19 cases by 77%. After controlling the CAO, it returned to monitor the imported-domestic transmission mode for Delta VOC. The Poisson-based epidemic surveillance model was applied to monitoring imported cases dominated by Delta VOC. The estimated results (table 1, Delta VOC period) show an increase in an imported case was at greater risk for the ensuing cluster infections by 10.16% (95% CrI 7.01% to 13.59%). is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021.10.19.21265107 doi: medRxiv preprint expected (green circle), the observed number of domestic cases is far below the threshold of outbreak. This can be attributed to the implementation of enhanced containment measures including the border control strategies strengthened by multiple tests on arrival and during quarantine, the collective quarantine strategy, and the elevated alerts of NPIs to level two and three since the CAO in May 2021 in Taiwan. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint While a series of cyclic CAOs in each country or region during covid -19 pandemic have been observed since 2020, it is imperative to avert such cyclic CAOs by developing the epidemic surveillance models for forestalling covid-19 epidemic through monitoring the possible spread of imported cases and for containing the spread of SARS-CoV-2 in the face of CAOs. By using the empirical data on imported and domestic covid-19 cases in Taiwan, the risk of weekly domestic cases resulting from one-week prior imported cases were estimated as 9.54% (95% CrI 6.44% to 12.59%), 14.14% (95% CrI 5.41% to 25.10%), and 10.16% (95% CrI 7.01% to 13.59%) for the wild type and D614G, Alpha VOC, and Delta VOC, respectively. A one-week-prior warning by using the upper bound of 95% CrI of the importeddomestic transmission were signaled to avert the resultant CAO based on these estimated results. Regarding the real time monitoring for the containment of CAOs, NPIs strengthened from 30% on 18 May, 2021 at the initial outbreak in Taiwan to more than 90% since 8 June were revealed, which contributed to the reduction of Rt form four to lower than one since then. The merit and the application of these two epidemic models are described as follows. Applying the first surveillance model for monitoring importation cases prior to is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint 10, 20, 23 and also using the duration from Rt larger than one to Rt smaller than one and case load following the machining learning model. 33 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021.10.19.21265107 doi: medRxiv preprint CAO between 9-12 May because of the increased transmissibility of Alpha VOC that was supported by the increased risk of imported-domestic transmission in comparison with the wild type and the D614G type (14.14% vs 9.54%, table 1). However, low level of NPIs might also make contribution to such a CAO around mid-May (40%, fig 4) . Regarding the Delta VOC period after stamping out CAO in relation to Alpha VOC in Taiwan, the level of NPI alert and the strict border control strategies implemented since the CAO period reduced the risk of imported-domestic transmission to 10.16% (table 1) to avert Delta VOC CAO. The application of the second SEIR model for monitoring the real-time operation of NPIs after scaling up alert provides a clue to whether, how, and when to contain CAOs with efficiency, particularly for VOCs. This is especially true for the illustration in Taiwan, since the mass vaccination was at the initial stage of rolling out period with an insufficient vaccine supply before and during the CAO in May 2021 in Taiwan. The CAO in relation to Alpha VOC in Taiwan was stamped out effectively through the implementation of NPIs by scaling up the nationwide alert level and the establishment of active surveillance at hotspots (supplementary figure 1 and figure 3 ). The real time monitoring for the implementation of NPIs can be also quantified by is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021.10.19.21265107 doi: medRxiv preprint using the SEIR-based surveillance model (fig 4) . In contrast to Taiwan, Israel demonstrated the effective containment of CAO by using mass vaccination. 31, 32 The impact of these two approaches, NPIs with testing and vaccination, on stamping out is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021.10.19.21265107 doi: medRxiv preprint and Qatar 35 after the mass vaccination program since early 2021 to monitor the impact of imported cases on the risk of domestic cluster infections. This is especially important for CAOs resulting from vaccine breakthrough in the country or region with high vaccine coverage or a well-controlled covid-19 attributed to strict NPIs reported worldwide. The former situation is noted in the recent Delta VOC outbreaks of Singapore 37 and Israel 38 after mass vaccination and the latter can refer to the classical example of Australia 39 with a well-controlled covid-19 via high level NPI alert for a long time. The second kind of surveillance model for CAO is to monitor whether, how, and when NPIs and community-based active surveillance with rapid test are effective in containing CAO. This surveillance model for CAO is very useful for countries that have lasting CAO and low supply of vaccine and rely mainly on NPIs as the main containment strategy. Namely, countries at their rolling out stage to raise vaccination coverage require such a support from the real-time surveillance of CAO to guide the implementation of appropriate NPIs to mitigate CAO with the balance of socioeconomical activities. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; • The CECC recommends the cancellation or postponement of non-essential gatherings that will bring people into close contact with others. • Businesses and public venues required to implement real-name registration, social distancing, temperature checks, and regular disinfection Domestically transmitted cases from unknown sources. • Fines imposed for those failure to follow mask guidelines. • Outdoor gatherings over 500 and indoor gatherings over 100 banned. • Public gatherings must implement social distancing, mask-wearing/partitions, an identificationbased registration system, temperature checks, crowd controls and routine disinfection or be cancelled. • Places of business must impose crowd controls; those unable to implement necessary epidemic prevention measures should temporarily suspend operations. • When necessary, the CECC may order the closure of entertainment or leisure-related businesses or public venues. Three community clusters within a week (or) ten domestically transmitted cases from unknown sources in one day. • Wearing mask at all times outdoors is mandatory. • Cancellation of outdoor gatherings of 10+ people and indoor gatherings of 5+ people. • All places of business and public venues are shuttered, with the exception of essential services, police departments, hospitals, and government buildings. • • People can only leave home for essential activities (ex. to purchase food, receive medical treatment, or for essential work) and must wear a mask and maintain a social distance at all times. • Masking and social distancing must be practiced at home. • All public events cancelled. • Apart from essential services, law enforcement, medical and government services, all in-person work and school are suspended. • Lockdowns will be imposed in counties, cities, or townships where an outbreak has become severe. Only designated persons may enter or leave these lockdown zones, and residents must stay in their homes . CC-BY-NC 4.0 International license It is made available under a perpetuity. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. March and 5 April 2020, which was followed by the peak of imported cases between 22 and 29 March 2020. Supplementary table 3 shows the association between domestic cases lagging one-week behind imported cases in New Zealand (DIC=1687.9), which is smaller than the model with concurrent-week imported cases (DIC=2173.2) and those lagging two-week behind imported cases (DIC=2395.4) (data not shown but available upon requests). It shows that an increase in one imported case would increase the risk of domestic cases by 9.38% (95% CI 8.88% to 9.86%). is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted October 23, 2021. ; https://doi.org/10.1101/2021.10.19.21265107 doi: medRxiv preprint An Index for Lifting Social Distancing During the COVID-19 Pandemic: Algorithm Recommendation for Lifting Social Distancing Estimated transmissibility and impact of SARS-CoV-2 lineage B.1.1.7 in England Usher Network for COVID-19 Evidence Reviews (UNCOVER) group. 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