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  1. Article ; Online: Modeling behavioral change and COVID-19 containment in Mexico: A trade-off between lockdown and compliance.

    Acuña-Zegarra, Manuel Adrian / Santana-Cibrian, Mario / Velasco-Hernandez, Jorge X

    Mathematical biosciences

    2020  Volume 325, Page(s) 108370

    Abstract: Sanitary Emergency Measures (SEM) were implemented in Mexico on March 30th, 2020 requiring the suspension of non-essential activities. This action followed a Healthy Distance Sanitary action on March 23rd, 2020. The aim of both measures was to reduce ... ...

    Abstract Sanitary Emergency Measures (SEM) were implemented in Mexico on March 30th, 2020 requiring the suspension of non-essential activities. This action followed a Healthy Distance Sanitary action on March 23rd, 2020. The aim of both measures was to reduce community transmission of COVID-19 in Mexico by lowering the effective contact rate. Using a modification of the Kermack-McKendrick SEIR model we explore the effect of behavioral changes required to lower community transmission by introducing a time-varying contact rate, and the consequences of disease spread in a population subject to suspension of non-essential activities. Our study shows that there exists a trade-off between the proportion of the population under SEM and the average time an individual is committed to all the behavioral changes needed to achieve an effective social distancing. This trade-off generates an optimum value for the proportion of the population under strict mitigation measures, significantly below 1 in some cases, that minimizes maximum COVID-19 incidence. We study the population-level impact of three key factors: the implementation of behavior change control measures, the time horizon necessary to reduce the effective contact rate and the proportion of people under SEM in combating COVID-19. Our model is fitted to the available data. The initial phase of the epidemic, from February 17th to March 23rd, 2020, is used to estimate the contact rates, infectious periods and mortality rate using both confirmed cases (by date of symptoms initiation), and daily mortality. Data on deaths after March 23rd, 2020 is used to estimate the mortality rate after the mitigation measures are implemented. Our simulations indicate that the most likely dates for maximum incidence are between late May and early June, 2020 under a scenario of high SEM compliance and low SEM abandonment rate.
    MeSH term(s) COVID-19 ; Communicable Disease Control ; Coronavirus Infections/prevention & control ; Health Behavior ; Humans ; Mexico ; Models, Theoretical ; Pandemics/prevention & control ; Pneumonia, Viral/prevention & control ; Risk Reduction Behavior ; Social Isolation
    Keywords covid19
    Language English
    Publishing date 2020-05-06
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 1126-5
    ISSN 1879-3134 ; 0025-5564
    ISSN (online) 1879-3134
    ISSN 0025-5564
    DOI 10.1016/j.mbs.2020.108370
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: COVID-19 optimal vaccination policies: A modeling study on efficacy, natural and vaccine-induced immunity responses.

    Acuña-Zegarra, Manuel Adrian / Díaz-Infante, Saúl / Baca-Carrasco, David / Olmos-Liceaga, Daniel

    Mathematical biosciences

    2021  Volume 337, Page(s) 108614

    Abstract: About a year into the pandemic, COVID-19 accumulates more than two million deaths worldwide. Despite non-pharmaceutical interventions such as social distance, mask-wearing, and restrictive lockdown, the daily confirmed cases remain growing. Vaccine ... ...

    Abstract About a year into the pandemic, COVID-19 accumulates more than two million deaths worldwide. Despite non-pharmaceutical interventions such as social distance, mask-wearing, and restrictive lockdown, the daily confirmed cases remain growing. Vaccine developments from Pfizer, Moderna, and Gamaleya Institute reach more than 90% efficacy and sustain the vaccination campaigns in multiple countries. However, natural and vaccine-induced immunity responses remain poorly understood. There are great expectations, but the new SARS-CoV-2 variants demand to inquire if the vaccines will be highly protective or induce permanent immunity. Further, in the first quarter of 2021, vaccine supply is scarce. Consequently, some countries that are applying the Pfizer vaccine will delay its second required dose. Likewise, logistic supply, economic and political implications impose a set of grand challenges to develop vaccination policies. Therefore, health decision-makers require tools to evaluate hypothetical scenarios and evaluate admissible responses. Following some of the WHO-SAGE recommendations, we formulate an optimal control problem with mixed constraints to describe vaccination schedules. Our solution identifies vaccination policies that minimize the burden of COVID-19 quantified by the number of disability-adjusted years of life lost. These optimal policies ensure the vaccination coverage of a prescribed population fraction in a given time horizon and preserve hospitalization occupancy below a risk level. We explore "via simulation" plausible scenarios regarding efficacy, coverage, vaccine-induced, and natural immunity. Our simulations suggest that response regarding vaccine-induced immunity and reinfection periods would play a dominant role in mitigating COVID-19.
    MeSH term(s) COVID-19/immunology ; COVID-19/prevention & control ; COVID-19 Vaccines/immunology ; COVID-19 Vaccines/pharmacology ; Humans ; Mass Vaccination/legislation & jurisprudence ; Mass Vaccination/standards ; Mass Vaccination/statistics & numerical data ; Models, Theoretical ; Outcome and Process Assessment, Health Care/statistics & numerical data
    Chemical Substances COVID-19 Vaccines
    Language English
    Publishing date 2021-05-04
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 1126-5
    ISSN 1879-3134 ; 0025-5564
    ISSN (online) 1879-3134
    ISSN 0025-5564
    DOI 10.1016/j.mbs.2021.108614
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: The role of animal grazing in the spread of Chagas disease.

    Acuña-Zegarra, Manuel Adrian / Olmos-Liceaga, Daniel / Velasco-Hernández, Jorge X

    Journal of theoretical biology

    2018  Volume 457, Page(s) 19–28

    Abstract: Chagas disease is an important neglected tropical disease which causes on average about 7000 deaths per year, and an estimated 25 million people risk of acquiring it. This illness is often found in rural areas, which are usually characterized by poverty ... ...

    Abstract Chagas disease is an important neglected tropical disease which causes on average about 7000 deaths per year, and an estimated 25 million people risk of acquiring it. This illness is often found in rural areas, which are usually characterized by poverty and presence of animals which act as reservoirs of the disease. Our main objective is to study the effect of animal grazing on the disease levels of the human population. For this purpose, we consider two environments (domestic and wild) where each one has permanent residents, and there is a proportion of animals that move between both environments due to grazing. This movement is modeled through the residence time in each environment. We analyze the proposed model and finally, we discuss the influence of domestic animals residence time on the disease level of human population.
    MeSH term(s) Animals ; Animals, Domestic/parasitology ; Chagas Disease/epidemiology ; Chagas Disease/transmission ; Herbivory ; Humans ; Insect Vectors/parasitology ; Models, Biological
    Language English
    Publishing date 2018-08-20
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 2972-5
    ISSN 1095-8541 ; 0022-5193
    ISSN (online) 1095-8541
    ISSN 0022-5193
    DOI 10.1016/j.jtbi.2018.08.025
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article ; Online: Modeling behavioral change and COVID-19 containment in Mexico

    Acuña-Zegarra, Manuel Adrian / Santana-Cibrian, Mario / Velasco-Hernandez, Jorge X.

    Mathematical Biosciences

    A trade-off between lockdown and compliance

    2020  Volume 325, Page(s) 108370

    Keywords General Biochemistry, Genetics and Molecular Biology ; Modelling and Simulation ; Statistics and Probability ; General Immunology and Microbiology ; Applied Mathematics ; General Agricultural and Biological Sciences ; General Medicine ; covid19
    Language English
    Publisher Elsevier BV
    Publishing country us
    Document type Article ; Online
    ZDB-ID 1126-5
    ISSN 1879-3134 ; 0025-5564
    ISSN (online) 1879-3134
    ISSN 0025-5564
    DOI 10.1016/j.mbs.2020.108370
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  5. Article: Modeling behavioral change and COVID-19 containment in Mexico: A trade-off between lockdown and compliance

    Acuña-Zegarra, Manuel Adrian / Santana-Cibrian, Mario / Velasco-Hernandez, Jorge X

    Math Biosci

    Abstract: Sanitary Emergency Measures (SEM) were implemented in Mexico on March 30th, 2020 requiring the suspension of non-essential activities. This action followed a Healthy Distance Sanitary action on March 23rd, 2020. The aim of both measures was to reduce ... ...

    Abstract Sanitary Emergency Measures (SEM) were implemented in Mexico on March 30th, 2020 requiring the suspension of non-essential activities. This action followed a Healthy Distance Sanitary action on March 23rd, 2020. The aim of both measures was to reduce community transmission of COVID-19 in Mexico by lowering the effective contact rate. Using a modification of the Kermack-McKendrick SEIR model we explore the effect of behavioral changes required to lower community transmission by introducing a time-varying contact rate, and the consequences of disease spread in a population subject to suspension of non-essential activities. Our study shows that there exists a trade-off between the proportion of the population under SEM and the average time an individual is committed to all the behavioral changes needed to achieve an effective social distancing. This trade-off generates an optimum value for the proportion of the population under strict mitigation measures, significantly below 1 in some cases, that minimizes maximum COVID-19 incidence. We study the population-level impact of three key factors: the implementation of behavior change control measures, the time horizon necessary to reduce the effective contact rate and the proportion of people under SEM in combating COVID-19. Our model is fitted to the available data. The initial phase of the epidemic, from February 17th to March 23rd, 2020, is used to estimate the contact rates, infectious periods and mortality rate using both confirmed cases (by date of symptoms initiation), and daily mortality. Data on deaths after March 23rd, 2020 is used to estimate the mortality rate after the mitigation measures are implemented. Our simulations indicate that the most likely dates for maximum incidence are between late May and early June, 2020 under a scenario of high SEM compliance and low SEM abandonment rate.
    Keywords covid19
    Publisher WHO
    Document type Article
    Note WHO #Covidence: #186431
    Database COVID19

    Kategorien

  6. Article ; Online: A methodology to generate epidemic scenarios for emerging infectious diseases based on the use of key calendar events

    Acuña-Zegarra, Manuel Adrian / Santana-Cibrian, Mario / Rodriguez Hernandez-Vela, Carlos E. / Mena, Ramsés H. / Velasco-Hernandez, Jorge X.

    medRxiv

    Abstract: This work presents a methodology to recreate the observed dynamics of emerging infectious diseases and to generate short-term forecasts for their evolution based on superspreading events occurring on key calendar dates. The method is illustrated by the ... ...

    Abstract This work presents a methodology to recreate the observed dynamics of emerging infectious diseases and to generate short-term forecasts for their evolution based on superspreading events occurring on key calendar dates. The method is illustrated by the COVID-19 pandemic dynamics in Mexico and Peru up to January 31, 2022. We also produce scenarios obtained through the estimation of a time-dependent contact rate, with the main assumption that the dynamic of the disease is determined by the mobility and social activity of the population during holidays and other important calendar dates. First, historical changes in the effective contact rate on predetermined dates are estimated. Then, this information is used to forecast scenarios under the assumption that the trends of the effective contact rate observed in the past will be similar on the same but future key calendar dates. All other conditions are assumed to remain constant in the time scale of the projections. One of the main features of the methodology is that it avoids the necessity of fixing values of the dynamic parameters for the whole prediction period. Results show that considering the key dates as reference information is useful to recreate the different outbreaks, slow or fast-growing, that an epidemic can present and, in most cases, make good short-term predictions.
    Keywords covid19
    Language English
    Publishing date 2022-05-01
    Publisher Cold Spring Harbor Laboratory Press
    Document type Article ; Online
    DOI 10.1101/2022.04.29.22274465
    Database COVID19

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  7. Article ; Online: Flattening the curve and the effect of atypical events on mitigation measures in Mexico: a modeling perspective

    Santana-Cibrian, Mario / Acuna-Zegarra, Manuel Adrian / Velasco-Hernandez, Jorge X.

    Abstract: On 23 and 30 March 2020 the Mexican Federal government implemented social distancing measures to mitigate the COVID-19 epidemic. We use a mathematical model to explore atypical transmission events within the confinement period, triggered by the timing ... ...

    Abstract On 23 and 30 March 2020 the Mexican Federal government implemented social distancing measures to mitigate the COVID-19 epidemic. We use a mathematical model to explore atypical transmission events within the confinement period, triggered by the timing and strength of short time perturbations of social distancing. We show that social distancing measures were successful in achieving a significant reduction of the effective contact rate in the early weeks of the intervention. However, "flattening the curve" had an undesirable effect, since the epidemic peak was delayed too far, almost to the government preset day for lifting restrictions (01 June 2020). If the peak indeed occurs in late May or early June, then the events of children's day and mother's day may either generate a later peak (worst case scenario), a long plateau with relatively constant but high incidence (middle case scenario) or the same peak date as in the original baseline epidemic curve, but with a post-peak interval of slower decay.
    Keywords covid19
    Publisher MedRxiv; WHO
    Document type Article ; Online
    Note WHO #Covidence: #20109678
    DOI 10.1101/2020.05.21.20109678
    Database COVID19

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  8. Article ; Online: Flattening the curve and the effect of atypical events on mitigation measures in Mexico: a modeling perspective

    Santana-Cibrian, Mario / Acuna-Zegarra, Manuel Adrian / Velasco-Hernandez, Jorge X.

    medRxiv

    Abstract: On 23 and 30 March 2020 the Mexican Federal government implemented social distancing measures to mitigate the COVID-19 epidemic. We use a mathematical model to explore atypical transmission events within the confinement period, triggered by the timing ... ...

    Abstract On 23 and 30 March 2020 the Mexican Federal government implemented social distancing measures to mitigate the COVID-19 epidemic. We use a mathematical model to explore atypical transmission events within the confinement period, triggered by the timing and strength of short time perturbations of social distancing. We show that social distancing measures were successful in achieving a significant reduction of the effective contact rate in the early weeks of the intervention. However, "flattening the curve" had an undesirable effect, since the epidemic peak was delayed too far, almost to the government preset day for lifting restrictions (01 June 2020). If the peak indeed occurs in late May or early June, then the events of children9s day and mother9s day may either generate a later peak (worst case scenario), a long plateau with relatively constant but high incidence (middle case scenario) or the same peak date as in the original baseline epidemic curve, but with a post-peak interval of slower decay.
    Keywords covid19
    Language English
    Publishing date 2020-05-23
    Publisher Cold Spring Harbor Laboratory Press
    Document type Article ; Online
    DOI 10.1101/2020.05.21.20109678
    Database COVID19

    Kategorien

  9. Article ; Online: COVID-19 optimal vaccination policies: a modeling study on efficacy, natural and vaccine-induced immunity responses

    Acuna-Zegarra, Manuel Adrian / Diaz-Infante, Saul / Baca-Carrasco, David / Olmos Liceaga, Daniel

    medRxiv

    Abstract: At the date, Europe and part of North America face the second wave of COVID-19, causing more than 1 300 000 deaths worldwide. Humanity lacks successful treatments, and a sustainable solution is an effective vaccine. Pfizer and the Russian Gamaleya ... ...

    Abstract At the date, Europe and part of North America face the second wave of COVID-19, causing more than 1 300 000 deaths worldwide. Humanity lacks successful treatments, and a sustainable solution is an effective vaccine. Pfizer and the Russian Gamaleya Institute report that its vaccines reach more than 90 % efficacy in a recent press release. If third stage trial results favorable, pharmaceutical firms estimate big scale production of its vaccine candidates around the first 2021 quarter and the World Health organization fix as objective, vaccinate 20 % of the whole population at the final of 2021. However, since COVID-19 is new to our knowledge, vaccine efficacy and induced-immunity responses remain poorly understood. There are great expectations, but few think the first vaccines will be fully protective. Instead, they may reduce the severity of illness, reducing hospitalization and death cases. Further, logistic supply, economic and political implications impose a set of grand challenges to develop vaccination policies. For this reason, health decision-makers require tools to evaluate hypothetical scenarios and evaluate admissible responses. Our contribution answers questions in this direction. According to the WHO Strategic Advisory Group of Experts on Immunization Working Group on COVID-19 Vaccines, we formulate an optimal controlled model to describe vaccination policies that minimize the burden of COVID-19 quantified by the number of disability-adjusted years of life lost. Additionally, we analyze the reproductive vaccination number according to vaccination profiles depending on coverage, efficacy, horizon time, and vaccination rate. We explore scenarios regarding efficacy, coverage, vaccine-induced immunity, and natural immunity via numerical simulation. Our results suggest that response regarding vaccine-induced immunity and natural immunity would play a dominant role in the vaccination policy design. Likewise, the vaccine efficacy would influence the time of intensifying the number of doses in the vaccination policy.
    Keywords covid19
    Language English
    Publishing date 2020-11-20
    Publisher Cold Spring Harbor Laboratory Press
    Document type Article ; Online
    DOI 10.1101/2020.11.19.20235176
    Database COVID19

    Kategorien

  10. Article ; Online: The SARS-CoV-2 epidemic outbreak: a review of plausible scenarios of containment and mitigation for Mexico

    Acuna-Zegarra, Manuel Adrian / Comas-Garcia, Andreu / Hernandez-Vargas, Esteban / Santana-Cibrian, Mario / Velasco-Hernandez, Jorge X.

    medRxiv

    Abstract: We present here several variants of a mathematical model to explore three main issues related to SARS-CoV-2 spread in scenarios similar to those present in Mexico and elsewhere in Latin America. We explore the consequences for travel inside a given ... ...

    Abstract We present here several variants of a mathematical model to explore three main issues related to SARS-CoV-2 spread in scenarios similar to those present in Mexico and elsewhere in Latin America. We explore the consequences for travel inside a given region, in this case Mexico, particularly focusing on airplane transportation but attempting to give a gross approximation to terrestrial movement since this is the main form of population movement across geographical areas in the country; then we proceed to study the effect of behavioral changes required to lower transmission by lowering the contact rate and infection probability and lastly, we explore the consequences of disease spread in a population subject to social isolation.These models are not suitable for predictive purposes although some rough predictions can be extracted from them. They are presented as a tool that can serve to explore plausible scenarios of spread and impact, effectiveness and consequences of contention and mitigation policies. Given the early stage at which the epidemic is at the date of writing in Mexico, we hope these ideas can be helpful for the understanding of the importance of isolation, social distancing and screening of the general population.
    Keywords covid19
    Language English
    Publishing date 2020-03-31
    Publisher Cold Spring Harbor Laboratory Press
    Document type Article ; Online
    DOI 10.1101/2020.03.28.20046276
    Database COVID19

    Kategorien

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