Assessing the mechanism of citywide test-trace-isolate Zero-COVID policy and exit strategy of COVID-19 pandemic

Background:Countries that aimed for eliminating the cases of COVID-19 with test-trace-isolate policy are found to have lower infections,deaths,and better economic performance,compared with those that opted for other mitigation strategies.However,the continuous evolution of new strains has raised the question of whether COVID-19 eradication is still possible given the limited public health response capacity and fatigue of the epidemic.We aim to investigate the mechanism of the Zero-COVID policy on outbreak containment,and to explore the possibility of eradication of Omicron transmission using the citywide test-trace-isolate(CTTI)strategy.Methods:We develop a compartmental model incorporating the CTTI Zero-COVID policy to understand how it contributes to the SARS-CoV-2 elimination.We employ our model to mimic the Delta outbreak in Fujian Province,China,from September 10 to October 9,2021,and the Omicron outbreak in Jilin Province,China for the period from March 1 to April 1,2022.Projections and sensitivity analyses were conducted using dynamical system and Latin Hypercube Sampling/Partial Rank Correlation Coefcient(PRCC).Results:Calibration results of the model estimate the Fujian Delta outbreak can end in 30(95%confdence interval CI:28–33)days,after 10(95%CI:9–11)rounds of citywide testing.The emerging Jilin Omicron outbreak may achieve zero COVID cases in 50(95%CI:41–57)days if supported with sufcient public health resources and population compliance,which shows the efectiveness of the CTTI Zero-COVID policy.Conclusions:The CTTI policy shows the capacity for the eradication of the Delta outbreaks and also the Omicron outbreaks.Nonetheless,the implementation of radical CTTI is challenging,which requires routine monitoring for early detection,adequate testing capacity,efcient contact tracing,and high isolation compliance,which constrain its benefts in regions with limited resources.Moreover,these challenges become even more acute in the face of more contagious variants with a high proportion of asymptomatic cases.Hence,in regions where CTTI is not possible,personal protection,public health control measures,and vaccination are indispensable for mitigating and exiting the COVID-19 pandemic.

RMB Exchange Rate Regime: Suggestions on Further Reform and Exit Strategy

Since 2000, the focus of the study of the RMB ex change rate has transferred from debate on whether it should appreciate or depreciate to the overall planning and the envisaged improvement of the RMB exchange rate regime.

Exit selection strategy in pedestrian evacuation simulation with multi-exits

A mixed strategy of the exit selection in a pedestrian evacuation simulation with multi-exits is constructed by fusing the distance-based and time-based strategies through a cognitive coefficient, in order to reduce the evacuation imbalance caused by the asymmetry of exits or pedestrian layout, to find a critical density to distinguish whether the strategy of exit selection takes effect or not, and to analyze the exit selection results with different cognitive coefficients. The strategy of exit selection is embedded in the computation of the shortest estimated distance in a dynamic parameter model, in which the concept of a jam area layer and the procedure of step-by-step expending are introduced. Simulation results indicate the characteristics of evacuation time gradually varying against cognitive coefficient and the effectiveness of reducing evacuation imbalance caused by the asymmetry of pedestrian or exit layout. It is found that there is a critical density to distinguish whether a pedestrian jam occurs in the evacuation and whether an exit selection strategy is in effect. It is also shown that the strategy of exit selection has no effect on the evacuation process in the no-effect phase with a low density, and that evacuation time and exit selection are dependent on the cognitive coefficient and pedestrian initial density in the in-effect phase with a high density.

Exit strategies in inflammatory bowel disease:Looking beyond antitumor necrosis factors

The long-term management of patients with inflammatory bowel disease(IBD)is still a matter of debate,and no clear guidelines have been issued.In clinical practice,gastroenterologists often have to deal with patients in prolonged remission after immunomodulatory or immunosuppressive therapies.When planning an exit strategy for drug withdrawal,the risk of disease relapse must be balanced against the risk of drug-related adverse events and healthcare costs.Furthermore,there is still a dearth of data on the withdrawal of novel biologics,such as the anti-α4β7 integrin antibody(vedolizumab)and anti-IL12/23 antibody(ustekinumab),as well as the small molecule tofacitinib.Models for estimating the risk of disease relapse and the efficacy of retreatment should be evaluated according to the patient's age and IBD phenotype.These models should guide clinicians in programming a temporary drug withdrawal after discussing realistic outcomes with the patient.This would shift the paradigm from an exit strategy to a holiday strategy.

A novel cascaded H-bridge photovoltaic inverter with flexible arc suppression function

This paper presents a novel approach that simultaneously enables photovoltaic(PV)inversion and flexible arc suppression during single-phase grounding faults.Inverters compensate for ground currents through an arc-elimination function,while outputting a PV direct current(DC)power supply.This method effectively reduces the residual grounding current.To reduce the dependence of the arc-suppression performance on accurate compensation current-injection models,an adaptive fuzzy neural network imitating a sliding mode controller was designed.An online adaptive adjustment law for network parameters was developed,based on the Lyapunov stability theorem,to improve the robustness of the inverter to fault and connection locations.Furthermore,a new arc-suppression control exit strategy is proposed to allow a zerosequence voltage amplitude to quickly and smoothly track a target value by controlling the nonlinear decrease in current and reducing the regulation time.Simulation results showed that the proposed method can effectively achieve fast arc suppression and reduce the fault impact current in single-phase grounding faults.Compared to other methods,the proposed method can generate a lower residual grounding current and maintain good arc-suppression performance under different transition resistances and fault locations.

Optimal Exit Layout Strategy for Crowd Safety Evacuation in a Ramp Domain

Pedestrian behavior modeling plays a considerably important role in improving operational efficiency and safety of pedestrian infrastructure.In this paper,we first propose a cost potential field cellular automata model that simulates crowd evacuation dynamics on a ramp with two exits.In the model,each pedestrian navigates according to the cost potential field in the ramp domain.Evacuation behaviors of pedestrians are investigated with respect to the ramp angle and the layout of the exits.An aggregated pushing force field is introduced to capture the effects of pushing interactions among pedestrians under congested situations.The phenomenon of pedestrians’falling down is modeled and demonstrated under various scenarios with different exit layouts and ramp angles.Numerical results show that an optimal layout strategy is to set the two exits in the center of the bottom and the top of the ramp,respectively.This typical exit layout design could effectively prevent and/or reduce crowd injury caused by the domino effect of pedestrians falling down in a stampede.

A four-compartment model for the COVID-19 infection—implications on infection kinetics,control measures,and lockdown exit strategies

Objective:To analyse the impact and repercussions of the surge in healthcare demand in response to the COVID-19 pandemic,assess the potential effectiveness of various infection/disease control measures,and make projections on the best approach to exit from the current lockdown.Design:A four-compartment model was constructed for SARS-CoV-2 infection based on the Wuhan data and validated with data collected in Italy,the UK,and the US.The model captures the effectiveness of various disease suppression measures in three modifiable factors:(a)the per capita contact rate(β)that can be lowered by means of social distancing,(b)infection probability upon contacting infectious individuals that can be lowered by wearing facemasks,personal hygiene,etc.,and(c)the population of infectious individuals in contact with the susceptible population,which can be lowered by quarantine.The model was used to make projections on the best approach to exit from the current lockdown.Results:The model was applied to evaluate the epidemiological data and hospital burden in Italy,the UK,and the US.The control measures were identified as the key drivers for the observed epidemiological data through sensitivity analyses.Analysing the different lockdown exit strategies showed that a lockdown exit strategy with a combination of social separation/general facemask use may work,but this needs to be supported by intense monitoring whichwould allowre-introduction/tightening of the controlmeasures if the number of newinfected subjects increases again.Conclusions and relevance:Governments should act early in a swift and decisive manner for containment policies.Any lockdown exit will need to be monitored closely,with regards to the potential of lockdown reimplementation.This mathematical model provides a framework for major pandemics in the future.

Projections of the transmission of the Omicron variant for Toronto,Ontario,and Canada using surveillance data following recent changes in testing policies

At the end of 2021,with the rapid escalation of COVID19 cases due to the Omicron variant,testing centers in Canada were overwhelmed.To alleviate the pressure on the PCR testing capacity,many provinces implemented new strategies that promote self testing and adjust the eligibility for PCR tests,making the count of new cases underreported.We designed a novel compartmental model which captures the new testing guidelines,social behaviours,booster vaccines campaign and features of the newest variant Omicron.To better describe the testing eligibility,we considered the population divided into high risk and non-highrisk settings.The model is calibrated using data from January 1 to February 9,2022,on cases and severe outcomes in Canada,the province of Ontario and City of Toronto.We conduct analyses on the impact of PCR testing capacity,self testing,different levels of reopening and vaccination coverage on cases and severe outcomes.Our results show that the total number of cases in Canada,Ontario and Toronto are 2.34(95%CI:1.22e3.38),2.20(95%CI:1.15e3.72),and 1.97(95%CI:1.13e3.41),times larger than reported cases,respectively.The current testing strategy is efficient if partial restrictions,such as limited capacity in public spaces,are implemented.Allowing more people to have access to PCR reduces the daily cases and severe outcomes;however,if PCR test capacity is insufficient,then it is important to promote self testing.Also,we found that reopening to a pre-pandemic level will lead to a resurgence of the infections,peaking in late March or April 2022.Vaccination and adherence to isolation protocols are important supports to the testing policies to mitigate any possible spread of the virus.