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      Use of contact tracing, isolation, and mass testing to control transmission of covid-19 in China

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          Abstract

          Qingwu Jiang and colleagues discuss China’s experience of contact tracing, isolation, and quarantine of infected people and their contacts, and mass nucleic acid testing in the second phase of the covid-19 epidemic

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          Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2)

          Estimation of the prevalence and contagiousness of undocumented novel coronavirus (SARS-CoV2) infections is critical for understanding the overall prevalence and pandemic potential of this disease. Here we use observations of reported infection within China, in conjunction with mobility data, a networked dynamic metapopulation model and Bayesian inference, to infer critical epidemiological characteristics associated with SARS-CoV2, including the fraction of undocumented infections and their contagiousness. We estimate 86% of all infections were undocumented (95% CI: [82%–90%]) prior to 23 January 2020 travel restrictions. Per person, the transmission rate of undocumented infections was 55% of documented infections ([46%–62%]), yet, due to their greater numbers, undocumented infections were the infection source for 79% of documented cases. These findings explain the rapid geographic spread of SARS-CoV2 and indicate containment of this virus will be particularly challenging.
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            Effectiveness of isolation, testing, contact tracing, and physical distancing on reducing transmission of SARS-CoV-2 in different settings: a mathematical modelling study

            Summary Background The isolation of symptomatic cases and tracing of contacts has been used as an early COVID-19 containment measure in many countries, with additional physical distancing measures also introduced as outbreaks have grown. To maintain control of infection while also reducing disruption to populations, there is a need to understand what combination of measures—including novel digital tracing approaches and less intensive physical distancing—might be required to reduce transmission. We aimed to estimate the reduction in transmission under different control measures across settings and how many contacts would be quarantined per day in different strategies for a given level of symptomatic case incidence. Methods For this mathematical modelling study, we used a model of individual-level transmission stratified by setting (household, work, school, or other) based on BBC Pandemic data from 40 162 UK participants. We simulated the effect of a range of different testing, isolation, tracing, and physical distancing scenarios. Under optimistic but plausible assumptions, we estimated reduction in the effective reproduction number and the number of contacts that would be newly quarantined each day under different strategies. Results We estimated that combined isolation and tracing strategies would reduce transmission more than mass testing or self-isolation alone: mean transmission reduction of 2% for mass random testing of 5% of the population each week, 29% for self-isolation alone of symptomatic cases within the household, 35% for self-isolation alone outside the household, 37% for self-isolation plus household quarantine, 64% for self-isolation and household quarantine with the addition of manual contact tracing of all contacts, 57% with the addition of manual tracing of acquaintances only, and 47% with the addition of app-based tracing only. If limits were placed on gatherings outside of home, school, or work, then manual contact tracing of acquaintances alone could have an effect on transmission reduction similar to that of detailed contact tracing. In a scenario where 1000 new symptomatic cases that met the definition to trigger contact tracing occurred per day, we estimated that, in most contact tracing strategies, 15 000–41 000 contacts would be newly quarantined each day. Interpretation Consistent with previous modelling studies and country-specific COVID-19 responses to date, our analysis estimated that a high proportion of cases would need to self-isolate and a high proportion of their contacts to be successfully traced to ensure an effective reproduction number lower than 1 in the absence of other measures. If combined with moderate physical distancing measures, self-isolation and contact tracing would be more likely to achieve control of severe acute respiratory syndrome coronavirus 2 transmission. Funding Wellcome Trust, UK Engineering and Physical Sciences Research Council, European Commission, Royal Society, Medical Research Council.
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              New Zealand eliminates COVID-19

              An aggressive approach has enabled New Zealand to end community transmission of SARS-CoV-2. Sophie Cousins reports. New Zealand recorded its first day of no new cases of coronavirus disease 2019 (COVID-19) early this week, more than a month after its strict lockdown began. At the time of publication, New Zealand had recorded fewer than 1500 confirmed cases of COVID-19, and 20 deaths. On March 23, a month after the country had recorded its first case, New Zealand committed to an elimination strategy. A few days later, Prime Minister Jacinda Ardern announced a strict national lockdown when it only had 102 cases and zero deaths. Her swift decision making won international praise, including from WHO. New Zealand's decision to pursue an elimination approach was a vastly different approach to usual pandemic planning, which has historically been based on a mitigation model and focuses on delaying the arrival of the virus, followed by a range of measures to flatten the curve of cases and deaths. Michael Baker, professor at the University of Otago's department of public health in Wellington, who has been advising the New Zealand Government on its response, said implementing a full lockdown—involving the closure of schools and non-essential workplaces, a ban on social gatherings, and severe travel restrictions—enabled the country to consider elimination. “I think it was the right decision; we had to go hard”, he said. “The two biggest benefits of pursuing an elimination strategy is that you have few cases and few deaths and you can get business back up and running. The alternative was that we are stuck with the virus and stuck between mitigation and suppression. Suppression is pretty grim.” While the strategy has had its critics, for Baker, the evidence was overwhelming that elimination could be achieved. Baker said the full lockdown allowed the country to get key systems up and running to effectively manage borders, and do contact tracing, testing, and surveillance. Since Jan 22, more than 150 000 people have been tested in a country of just 5 million. Testing has been focused on people with symptoms, with tracing of both close contacts and casual contacts. However, more widespread testing is now being introduced. The Ministry of Health is in discussion with districts to arrange testing of specific communities who are at higher risk of acquiring the virus such as those in aged residential care and health-care workers. Testing samples from sewerage is also being considered to monitor control and elimination. The response has also been one that placed science, leadership, and careful language at the forefront. Siouxsie Wiles, associate professor and head of the Bioluminescent Superbugs Lab at the University of Auckland, said one of the country's key successes has been the way in which COVID-19 was framed to the general population. “In other countries, people have been talking about war and battle, which puts people in a negative and fearful frame of mind”, she said. “The official response here has been guided by the principle that you do not stigmatise and that we unite against COVID-19.” Ardern has regularly appeared on social media, smiling and sharing parts of her personal life under lockdown but without underplaying the seriousness of the situation, which has helped to build public trust. Baker agreed that language was a crucial part of the response. He said that how the country communicates the concept of elimination will be important going forwards. Wiles agreed. “We don't want the public to feel like they are being lied to. Elimination to everyone means that it is gone. But in epidemiological terms, it means bringing cases down to zero or near zero in a geographical location. We will still see cases…but only cases in people who have arrived from overseas.” Travellers from abroad will be quarantined as part of efforts to prevent transmission in New Zealand. As New Zealand now eases its restrictions and its economy slowly reopens, there are discussions about how it can open up its borders while ensuring that everyone is protected, particularly susceptible populations. Australia, which is having similar success to New Zealand but is not publicly floating the idea of elimination, has been in discussion with its neighbour about reopening travel between the two countries. Baker envisions that, in time, a small number of countries in the region will reach an agreement to enable travel with specific control measures in place. Officials have pleaded for vigilance as breaches of the shutdown rules continue to rise. When the country loosened some of its restrictions last week, some fast-food outlets ran out of food as people flocked in huge numbers to get burgers and fries. “We are nearly there. We are not at the finish line yet”, Wiles said. “We won't see how successful we have been for a few weeks yet.”
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                Author and article information

                Contributors
                Role: professor
                Role: researcher
                Role: professor
                Role: researcher
                Role: professor
                Role: professor
                Journal
                BMJ
                BMJ
                BMJ-UK
                bmj
                The BMJ
                BMJ Publishing Group Ltd.
                0959-8138
                1756-1833
                2021
                02 December 2021
                : 375
                : n2330
                Affiliations
                [1 ]Fudan University School of Public Health, Shanghai, China
                [2 ]Key Laboratory of Public Health Safety, Fudan University, Ministry of Education, Shanghai, China
                [3 ]Fudan University Centre for Tropical Disease Research, Shanghai, China
                [4 ]Beijing Centre for Disease Prevention and Control and Beijing Research Centre for Preventive Medicine, Beijing, China
                [5 ]Xuhui Centre for Disease Control and Prevention, Shanghai, China
                [6 ]School of Epidemiology and Public Health, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
                Author notes
                Correspondence to: Q Jiang jiangqw@ 123456fudan.edu.cn
                Article
                zhou066127
                10.1136/bmj.n2330
                8634363
                34853002
                df24322a-1dd4-499d-b82c-82aeafac003c
                © Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

                This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

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                China’s Response to Covid-19

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