Modeling the Potential Impact of Norovirus Vaccination Among DoD Forces

ABSTRACT Introduction Norovirus, a contagious disease that spreads rapidly in close-quartered communities, has a debilitating effect in military settings, affecting troops’ health, productivity, and mission-readiness. This research presents a model of norovirus transmission, testing the vaccination’s effectiveness in military training centers. Methods Transmission was modeled using structured ordinary differential equations, including symptomatic and asymptomatic infection, genetic resistance, vaccination, and herd-immunity effects, within a hypothetical cohort of trainees and support staff. The modeled vaccine had an efficacy of 72%, 4 weeks after a single dose in phase 2 clinical trials. The transmission model was calibrated against data from a norovirus outbreak in a university setting. Sensitivity and uncertainty analyses were performed on 22 parameters. Results The greatest reduction in norovirus cases resulted from prophylactic environmental decontamination and vaccination of trainee and staff populations. These combined interventions prevented more than 6,800 cases of norovirus over the 10-year simulated period—a 15% reduction over the baseline scenario of no interventions. Implementing vaccination and environmental decontamination with an outbreak response threshold of 0.1%, prevented more than 5,300 infections; raising the threshold to 0.2% to 0.5% significantly reduced effectiveness. Environmental decontamination and contact reduction alone had little impact on overall norovirus cases. Conclusions Given vaccine characteristics, the model predicted that up to 15% of norovirus cases occurring in training settings over a 10-year period could be prevented by vaccinating all trainees and staff members immediately upon arrival on-base combined with continuous environmental decontamination. There was an impact on morbidity from implementing vaccination of trainees, alone and in combination with staff members. However, vaccinating staff alone prevented few cases over the simulation period, indicating the importance of trainees in norovirus transmission. Likewise, the negligible impact of environmental decontamination or contact reduction alone highlights the importance of addressing both person-to-person and environmental transmission together to minimize illnesses and training downtime.

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SARS-CoV-2 Herd Immunity of the Kyrgyz Population in 2021

10.21203/rs.3.rs-1138128/v1 ◽

2021 ◽

Author(s):

Anna Y. Popova ◽

Omor T. Kasymov ◽

Vyacheslav Y. Smolenski ◽

Вячеслав Смирнов ◽

Svetlana A. Egorova ◽

...

Keyword(s):

Randomized Study ◽

Herd Immunity ◽

Statistical Processing ◽

Cloud Service ◽

Asymptomatic Infection ◽

Enzyme Linked Immunosorbent Assay ◽

Pasteur Institute ◽

Cross Sectional ◽

Saint Petersburg ◽

Kyrgyz Population

Abstract Background. In the fight against coronavirus infection, an important direction is control of herd immunity to the pathogen. SARS-CoV-2 herd immunity is formed naturally as a result of manifest or asymptomatic infection, or artificially as a result of vaccination Aim: To assess the SARS-CoV-2 herd immunity status of the Kyrgyz population. Materials and methods. A cross-sectional, randomized study of SARS-CoV-2 herd immunity was carried out according to a program developed by Rospotrebnadzor, with the participation of the Saint Petersburg Pasteur Institute, taking into account WHO recommendations. In all study stages cloud service (internet) technologies were used. The ethics committees of the Preventive Medicine Association (Kyrgyzstan) and the Saint Petersburg Pasteur Institute (Russia) approved the study. A total of 9,471 volunteers were selected, representing 0.15% (95% CI 0.14-0.15) of the total population. They were randomized according to age and region. Antibodies (Abs) to the nucleocapsid antigen (Nag) were determined by enzyme-linked immunosorbent assay (ELISA) of volunteer blood plasma. For vaccinated individuals, Abs to the SARS-CoV-2 receptor-binding domain antigen (RBDag) were determined. Statistical processing of the results was carried out using Excel 2010 and other programs. Differences were designated as statistically significant at p<0.05. Results. The seroprevalence of the general population was 48.7% (95% CI 47.7-49.7), with a maximum in the group of '60-69 year old' (59.2% (56.6-61.7)) and a minimum in the group '1-17 y.o.' (32.7% (95 CI 29.4-36.1)). The largest proportion seropositive was found in the Chui region (51.3% (95% CI 47.9-54.8)). The lowest was in Osh city (38.1% (95 CI 32.6-43.9)). The maximum seropositivity was detected among healthcare workers (57.1% (95% CI 55.4-58.8); the minimum was noted among artists (38.6% (95% CI 26.0-52.4)). Asymptomatic SARS-CoV-2 positivity was 79.1% (96% CI 77.9-80.3). Vaccination with Sputnik V, EpiVacCorona, or Sinopharm formed comparable levels of immunity. Conclusions. The herd immunity to SARS-CoV-2 Nag is 48.75% (95% CI 47.7-49.7), and the overall immunity (Nag + RBDag) is 57%.

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The attainment of herd immunity with a reducing risk of contact infection in modelling

10.21203/rs.3.rs-289776/v4 ◽

2021 ◽

Author(s):

Kian Boon Law ◽

Kalaiarasu M Peariasamy ◽

Hishamshah Ibrahim ◽

Noor Hisham Abdullah

Keyword(s):

Infectious Disease ◽

Disease Transmission ◽

Herd Immunity ◽

Sir Model ◽

Mixed Population ◽

Transmission Model ◽

Force Of Infection ◽

Initial Stage ◽

And Control ◽

Model Features

Abstract The risk of contact infection among susceptible individuals in a randomly mixed population can be reduced by the presence of immune individuals and this principle forms the fundamental of herd immunity. The conventional susceptible-infectious-recovered (SIR) model features an infection-induced herd immunity model, but does not include the reducing risk of contact infection among susceptible individuals in the transmission model, therefore tends to overestimate the transmission dynamics of infectious diseases. Here we show that the reducing risk of contact infection among susceptible individuals can be achieved by incorporating the proportion of susceptible individuals (model A) or the inverse of proportion of recovered individuals (model B) in the force of infection of the SIR model. We numerically simulated the conventional SIR model and both new SIR models A and B under the exact condition with a basic reproduction number of 3·0. Prior to the numerical simulation, the threshold for the eradication of infectious disease through herd immunity was expected to be 0·667 (66·7%) for all three models. All three models performed likewise at the initial stage of disease transmission. In the conventional SIR model, the infectious disease subsided when 94·0 % of the population had been infected and recovered, way above the expected threshold for eradication and control of the infectious disease. Both models A and B simulated the infectious disease to diminish when 66·7% and 75·6% of the population had been infected, showing herd immunity might protect more susceptible individuals from the infectious disease as compared to the projection generated by the conventional SIR. Our study shows that model A provides a better framework for modelling herd immunity through vaccination, while model B provides a better framework for modelling herd immunity through infection. Both models overcome the insufficiency of the conventional SIR model in attaining the effect of herd immunity in modelling outputs, which is important and relevant for modelling infectious disease, such as the COVID-19 in a randomly mixed population.

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Effectiveness of Screening Hospital Admissions to Detect Asymptomatic Carriers of Clostridium difficile: A Modeling Evaluation

Infection Control and Hospital Epidemiology ◽

10.1086/677162 ◽

2014 ◽

Vol 35 (8) ◽

pp. 1043-1050 ◽

Cited By ~ 39

Author(s):

Cristina Lanzas ◽

Erik R. Dubberke

Keyword(s):

Clostridium Difficile ◽

Hospital Admissions ◽

Control Strategies ◽

Turnaround Time ◽

Current Control ◽

Hospital Ward ◽

Transmission Model ◽

Baseline Scenario ◽

Asymptomatic Carriers ◽

Contact Precautions

ObjectiveBoth asymptomatic and symptomatic Clostridium difficile carriers contribute to new colonizations and infections within a hospital, but current control strategies focus only on preventing transmission from symptomatic carriers. Our objective was to evaluate the potential effectiveness of methods targeting asymptomatic carriers to control C. difficile colonization and infection (CDI) rates in a hospital ward: screening patients at admission to detect asymptomatic C. difficile carriers and placing positive patients into contact precautions.MethodsWe developed an agent-based transmission model for C. difficile that incorporates screening and contact precautions for asymptomatic carriers in a hospital ward. We simulated scenarios that vary according to screening test characteristics, colonization prevalence, and type of strain present at admission.ResultsIn our baseline scenario, on average, 42% of CDI cases were community-onset cases. Within the hospital-onset (HO) cases, approximately half were patients admitted as asymptomatic carriers who became symptomatic in the ward. On average, testing for asymptomatic carriers reduced the number of new colonizations and HO-CDI cases by 40%–50% and 10%–25%, respectively, compared with the baseline scenario. Test sensitivity, turnaround time, colonization prevalence at admission, and strain type had significant effects on testing efficacy.ConclusionsTesting for asymptomatic carriers at admission may reduce both the number of new colonizations and HO-CDI cases. Additional reductions could be achieved by preventing disease in patients who are admitted as asymptomatic carriers and developed CDI during the hospital stay.

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Collective immunity to SARS-CoV-2 of Moscow residents during the COVID-19 epidemic period

Infekcionnye bolezni ◽

10.20953/1729-9225-2020-4-8-16 ◽

2020 ◽

Vol 18 (4) ◽

pp. 8-16

Author(s):

A.Yu. Popova ◽

◽

E.B. Yezhlova ◽

A.A. Melnikova ◽

E.E. Andreeva ◽

...

Keyword(s):

Herd Immunity ◽

Age Groups ◽

Asymptomatic Infection ◽

Administrative District ◽

Cultural Workers ◽

Population Immunity ◽

The North ◽

First Case ◽

Epidemic Period ◽

Structure Of Population

The coronavirus disease pandemic (COVID-19) was announced by WHO in February 2020. In Moscow, the first case of the disease was detected on March 2, 2020 in a man who arrived from Italy. Two weeks after the first case, there was an exponential increase in the number of cases. The incidence peaked in the 19th week of the year, followed by a steady decline, lasting 16 weeks. Objective. To investigate the level and structure of population immunity to the SARS-CoV-2 virus among the population of Moscow against the background of the incidence of COVID-19. Patients and methods. The study of population immunity of Moscow residents to SARS-CoV-2 was carried out in the period from July 1, 2020 to July 30, 2020 against the background of stabilization of the incidence rate. The work was conducted as part of the first stage of the Rospotrebnadzor project to assess population immunity to the SARS-CoV-2 virus among the population of the Russian Federation, taking into account the protocol recommended by WHO. Volunteers for the study were selected by the method of questioning and randomization. The results of the survey of 2688 people were included in the analysis. The number of volunteers in all age groups was 384–385 people. The content of specific IgG to the SARS-CoV-2 nucleocapsid was determined by the enzyme-linked immunosorbent assya using a kit produced by FBIS SRCAMB according to the manufacturer's instructions. Results. During the survey of volunteers it was found that the share of seroprevalent residents of Moscow was 22.1%. By age groups, the highest proportion of seroprevalent was found among children aged 14–17 years (44.6%), the lowest (15.9%) – among people aged 18–29 years. Seroprevalence had no gender differences. The lowest level of herd immunity was revealed in the North-Western Administrative District (16.8%), the highest – in the South-Eastern Administrative District, as well as in the Troitsky and Novomoskovsky Administrative Districts of Moscow (in both, 24.1%). The smallest number of seropositive persons was among cultural workers (5.8%), the largest – among medical workers (27.0%). In the presence of contacts with patients with COVID-19, the probability of seroconversion increases by 1.5 times, and among convalescing persons COVID-19 antibodies were detected in 60.0% of cases. The proportion of people with asymptomatic infection among seropositive residents was 82.4%. Conclusion. The results obtained make it possible to characterize the population immunity of Moscow residents and are essential for the planning and implementation of anti-epidemic measures during the incidence of COVID-19. Key words: coronaviruses, SARS-CoV-2, seroprevalence, population, COVID-19

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A simulation study on the relative role of age groups under differing pertussis transmission scenarios

10.1101/247007 ◽

2018 ◽

Cited By ~ 2

Author(s):

Ana I. Bento ◽

Aaron A. King ◽

Pejman Rohani

Keyword(s):

Herd Immunity ◽

Age Groups ◽

Transmission Model ◽

Relative Role ◽

Older Individuals ◽

Age Cohorts ◽

Relative Risks ◽

Transmission Mechanisms ◽

Acellular Vaccines ◽

The Impact

AbstractPertussis has resurged in many countries where it was once regarded as under control, with the recent outbreaks showing a shift in incidence towards teens and older individuals. Here, using an age-stratified transmission model, we tested two potential causes for underlying changes in pertussis transmission dynamics. We did so assuming hypothesized mechanisms supporting present-day pertussis epidemiology: (I) improved diagnostics, (II) acellular vaccines leading to asymptomatic transmission (III) both. We used the relative risks and odds ratio methods to examine the impact of these differing assumptions on signatures of relative roles of key age groups through time, allowing us to explore those age cohorts that disproportionately account for transmission. Our findings show that for epidemics after the vaccine switch, a scenario with increased adult reporting and no asymptomatic transmission reflect a loss of signal, where no age group appears to be key. While scenarios with asymptomatic transmission, reflect a population where children (1-10 years old) are still disproportionally at risk. These results demonstrate that understanding the underlying transmission mechanisms in a population are paramount for vaccination policies in attaining herd immunity and eventually eradication.

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Modelling infectious diseases with herd immunity in a randomly mixed population

10.21203/rs.3.rs-289776/v7 ◽

2021 ◽

Author(s):

Kian Boon Law ◽

Kalaiarasu M. Peariasamy ◽

Hishamshah Mohd. Ibrahim ◽

Noor Hisham Abdullah

Keyword(s):

Infectious Disease ◽

Infectious Diseases ◽

Transmission Rate ◽

Herd Immunity ◽

Sir Model ◽

Mixed Population ◽

Transmission Dynamics ◽

Transmission Model ◽

Infection Model ◽

Vaccination Rates

Abstract Background The conventional susceptible-infectious-recovered (SIR) model tends to overestimate the transmission dynamics of infectious diseases and ends up with total infections and total immunized population exceeding the threshold required for control and eradication of infectious diseases. The study aims to overcome the limitation by allowing the transmission rate of infectious disease to decline along with the reducing risk of contact infection. Methods Two new SIR models were developed to mimic the declining transmission rate of infectious diseases at different stages of transmission. Model A mimicked the declining transmission rate along with the reducing risk of transmission following infection, while Model B mimicked the declining transmission rate following recovery. Then, the conventional SIR model, Model A and Model B were used to simulate an infectious disease with a basic reproduction number (r0) of 3.0 and a herd immunity threshold (HIT) of 0.667 with and without vaccination. The infectious disease was expected to be controlled or eradicated when the total immunized population either through infection or vaccination reached the level predicted by the HIT. Outcomes of simulations were assessed at the time when the total immunized population reached the level predicted by the HIT, and at the end of simulations. Findings All three models performed likewise at the beginning of the transmission when sizes of infectious and recovered were relatively small as compared with the population size. The infectious disease modelled using the conventional SIR model appeared completely out of control even when the HIT was achieved in all scenarios with and without vaccination. The infectious disease modelled using Model A appeared to be controlled at the level predicted by the HIT in all scenarios with and without vaccination. Model B projected the infectious disease to be controlled at the level predicted by the HIT only at high vaccination rates. At lower vaccination rates or without vaccination, the level at which the infectious disease was controlled cannot be accurately predicted by the HIT. Conclusion Transmission dynamics of infectious diseases with herd immunity can accurately be modelled by allowing the transmission rate of infectious disease to decline along with the combined risk of contact infection. Model B provides a more credible framework for modelling infectious diseases with herd immunity in a randomly mixed population.

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Prevention of COVID-19 by mRNA-based vaccines within the general population of California

Clinical Infectious Diseases ◽

10.1093/cid/ciab640 ◽

2021 ◽

Author(s):

Kristin L Andrejko ◽

Jake Pry ◽

Jennifer F Myers ◽

Nicholas P Jewell ◽

John Openshaw ◽

...

Keyword(s):

General Population ◽

Herd Immunity ◽

Asymptomatic Infection ◽

Geographic Region ◽

Vaccine Effectiveness ◽

Vaccine Hesitancy ◽

Molecular Diagnostic ◽

California Department ◽

Molecular Diagnostic Test ◽

To Receive

Abstract Background Estimates of COVID-19 vaccine effectiveness under real-world conditions, and understanding of barriers to uptake, are necessary to inform vaccine rollout. Methods We enrolled cases (testing positive) and controls (testing negative) from among the population whose SARS-CoV-2 molecular diagnostic test results from 24 February-29 April 2021 were reported to the California Department of Public Health. Participants were matched on age, sex, and geographic region. We assessed participants’ self-reported history of mRNA-based COVID-19 vaccine receipt (BNT162b2 and mRNA-1273). Participants were considered fully vaccinated two weeks after second dose receipt. Among unvaccinated participants, we assessed willingness to receive vaccination. We measured vaccine effectiveness (VE) via the matched odds ratio of prior vaccination, comparing cases with controls. Results We enrolled 1023 eligible participants aged ≥18 years. Among 525 cases, 71 (13.5%) received BNT162b2 or mRNA-1273; 20 (3.8%) were fully vaccinated with either product. Among 498 controls, 185 (37.1%) received BNT162b2 or mRNA-1273; 86 (16.3%) were fully vaccinated with either product. Two weeks after second dose receipt, VE was 87.0% (95% confidence interval: 68.6-94.6%) and 86.2% (68.4-93.9%) for BNT162b2 and mRNA-1273, respectively. Fully vaccinated participants receiving either product experienced 91.3% (79.3-96.3%) and 68.3% (27.9-85.7%) VE against symptomatic and asymptomatic infection, respectively. Among unvaccinated participants, 42.4% (159/375) residing in rural regions and 23.8% (67/281) residing in urban regions reported hesitancy to receive COVID-19 vaccination. Conclusions Authorized mRNA-based vaccines are effective at reducing documented SARS-CoV-2 infections within the general population of California. Vaccine hesitancy presents a barrier to reaching coverage levels needed for herd immunity.

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Modeling Zika Vaccination Combined With Vector Interventions in DoD Populations

Military Medicine ◽

10.1093/milmed/usaa340 ◽

2021 ◽

Vol 186 (Supplement_1) ◽

pp. 82-90

Author(s):

Colleen Burgess ◽

Lis Nelis ◽

Cassie Huang

Keyword(s):

Mosquito Control ◽

Cost Benefit Analysis ◽

Herd Immunity ◽

Febrile Illness ◽

Sensitivity Analyses ◽

Transmission Model ◽

Model Parameters ◽

Military Installations ◽

Low Level ◽

Limited Effectiveness

ABSTRACT Introduction Zika virus (ZIKV) is a mild febrile illness generally transmitted via the bite of infected Aedes species mosquitoes, including Aedes aegypti, with the potential to cause neurological complications. Nearly 200 U.S. military installations are located within areas where Aedes mosquitos are found, putting thousands of personnel at risk for infection with ZIKV. This analysis aims to quantify the benefits of interventions, including vaccination, to decrease the risk of ZIKV on U.S. military installations. Methods The authors developed a dynamic transmission model to test the “effectiveness” of vaccination, personal protective measures (PPM), and mosquito control at reducing morbidity within U.S. military populations. ZIKV transmission was modeled as a compartmental susceptible-exposed-infected-recovered model tracking interactions between humans and mosquitos and incorporating seasonality of mosquito populations and the potential for herd immunity. The model included two-dose vaccination as well as symptomatic and asymptomatic infection. The model was calibrated against 2016 public health data in Puerto Rico; sensitivity analyses were performed on model parameters and interventions. Results The greatest reduction in total modeled ZIKV cases resulted from vaccination combined with mosquito control and PPM. All three interventions at their highest estimated level of efficiency reduced ZIKV cases by 99.9% over the baseline case of low-level adherence to PPM. The addition of vaccination had limited additional benefit over effective vector control and PPM since the significant lag to vaccine-induced protection limited effectiveness of vaccination. Conclusions Given the current vaccine, the model predicted that up to 92.8% of Zika cases occurring in deployment settings over a 10-year period could be prevented by adding vaccination to current low-level PPM. Combining vaccination with other interventions can reduce cases further. A location-specific cost-benefit analysis would be a valuable contribution to outbreak control policy as it could evaluate the economic impact of the interventions versus the reduced level of illness and downtime in this setting.

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Epidemiological and ecological determinants of Zika virus transmission in an urban setting

10.1101/101972 ◽

2017 ◽

Cited By ~ 2

Author(s):

J Lourenço ◽

M Maia de Lima ◽

NR Faria ◽

A Walker ◽

MUG Kraemer ◽

...

Keyword(s):

Herd Immunity ◽

Virus Transmission ◽

Urban Setting ◽

Health Concern ◽

Transmission Model ◽

Surveillance Systems ◽

Global Public Health ◽

Transmission Potential ◽

Near Future ◽

The City

AbstractZika has emerged as a global public health concern. Although its rapid geographic expansion can be attributed to the success of its Aedes mosquito vectors, local epidemiological drivers are still poorly understood. The city of Feira de Santana played a pivotal role in the early phases of the Chikungunya and Zika epidemics in Brazil. Here, using a climate-driven transmission model, we show that low Zika observation rates and a high vectorial capacity in this region were responsible for a high attack rate during the 2015 outbreak and the subsequent decline in cases in 2016, when the epidemic was peaking in the rest of the country. Our projections indicate that the balance between the loss of herd-immunity and the frequency of viral re-importation will dictate the transmission potential of Zika in this region in the near future. Sporadic outbreaks are expected but unlikely to be detected under current surveillance systems.

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Projecting the end of the Zika virus epidemic in Latin America: a modelling analysis

10.1101/323915 ◽

2018 ◽

Cited By ~ 1

Author(s):

Kathleen M O’Reilly ◽

Rachel Lowe ◽

W John Edmunds ◽

Philippe Mayaud ◽

Adam Kucharski ◽

...

Keyword(s):

Latin America ◽

Zika Virus ◽

Herd Immunity ◽

Reporting Rate ◽

World Health ◽

Transmission Model ◽

Parameter Estimates ◽

Model Parameters ◽

Spatio Temporal ◽

Reporting Rates

AbstractBackground Zika virus (ZIKV) emerged in Latin America & the Caribbean (LAC) region in 2013, and has had serious implications for population health in the region. In 2016, the World Health Organization declared the ZIKV outbreak a Public Health Emergency of International Concern following a cluster of associated neurological disorders and neonatal malformations. In 2017, Zika cases declined, but future incidence in LAC remains uncertain due to gaps in our understanding, considerable variation in surveillance and a lack of a comprehensive collation of data from affected countries.Methods Our analysis combines information on confirmed and suspected Zika cases across LAC countries and a spatio-temporal dynamic transmission model for ZIKV infection to determine key transmission parameters and projected incidence in 91 major cities within 35 countries. Seasonality was determined by spatio-temporal estimates of Aedes aegypti vector capacity. We used country and state-level data from 2015 to mid-2017 to infer key model parameters, country-specific disease reporting rates, and the 2018 projected incidence. A 10-fold cross-validation approach was used to validate parameter estimates to out-of-sample epidemic trajectories.Results There was limited transmission in 2015, but in 2016 and 2017 there was sufficient opportunity for wide-spread ZIKV transmission in most cities, resulting in the depletion of susceptible individuals. We predict that the highest number of cases in 2018 within some Brazilian States (Sao Paulo and Rio de Janeiro), Colombia and French Guiana, but the estimated number of cases were no more than a few hundred. Model estimates of the timing of the peak in incidence were correlated (p<0.05) with the reported peak in incidence. The reporting rate varied across countries, with lower reporting rates for those with only confirmed cases compared to those who reported both confirmed and suspected cases.Conclusions The findings suggest that the ZIKV epidemic is by and large over, with incidence projected to be low in most cities in LAC in 2018. Local low levels of transmission are probable but the estimated rate of infection suggests that most cities have a population with high levels of herd immunity.

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