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.

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.

The transmission of dengue virus with Aedes aegypti mosquito in a heterogeneous environment

This paper deals with dengue virus transmitted by the mosquito Aedes aegypti.A reaction-diffusion model is proposed incorporating both human and the A.aegypti population,where we divided mosquitoes into two sub-populations:the winged population and an aquatic form,with the winged mosquito population divided into the susceptible and infected classes.The threshold Qo depending on spatial heterogeneity is introduced for the mosquito population.Moreover,we introduce the basic reproduction number Rq for the infected classes,as well as its analytical properties.Qo and Ho are utilized to investigate the stability of the mosquito-established equilibriums.Our results show that the mosquitoes persist if Qo>1,while the transmission of dengue virus depends on the condition whether Ho<1 or Ho>1.

When and How to Adjust Non-Pharmacological Interventions Concurrent with Booster Vaccinations Against COVID-19—Guangdong,China,2022

Introduction:With the large-scale roll-out of the coronavirus disease 2019(COVID-19)booster vaccination effort(a vaccine dose given 6 months after completing primary vaccination)in China,we explore when and how China could lift non-pharmacological interventions(NPIs)against COVID-19 in 2022.Methods:Using a modified susceptible-infectiousrecovered(SIR)mathematical model,we projected the COVID-19 epidemic situation and required medical resources in Guangdong Province,China.Results:If the number of people entering from overseas recovers to 20%of the number in 2019,the epidemic in 2022 could be controlled at a low level by a containment(215 local cases)or suppression strategy(1,397 local cases).A mitigation strategy would lead to 21,722 local cases.A coexistence strategy would lead to a large epidemic with 6,850,083 local cases that would overwhelm Guangdong’s medical system.With 50%or 100%recovery of the 2019 level of travelers from overseas,the epidemic could also be controlled with containment or suppression,but enormous resources,including more hotel rooms for border quarantine,will be required.However,coexistence would lead to an uncontrollable epidemic with 12,922,032 local cases.Discussion:With booster vaccinations,the number of travelers from overseas could increase slightly in 2022,but a suppression strategy would need to be maintained to ensure a controllable epidemic.