scholarly journals Mathematical modeling of endemic cholera transmission

2021 ◽  
Author(s):  
Dennis L Chao
Keyword(s):  
Mathematical Modeling ◽  
Herd Immunity ◽  
Population Level ◽  
Additional Benefit ◽  
Mass Vaccination ◽  
The Cost ◽  
Vaccination Campaigns ◽  
The Impact ◽  
Indirect Protection ◽  
Endemic Cholera

Abstract Mathematical modeling can be used to project the impact of mass vaccination on cholera transmission. Here, we discuss two examples for which indirect protection from mass vaccination needs to be considered. In the first, we show that non-vaccinees can be protected by mass vaccination campaigns. This additional benefit of indirect protection improves the cost-effectiveness of mass vaccination. In the second, we model the use of mass vaccination to eliminate cholera. In this case, a high population level of immunity, including contributions from infection and vaccination, is required to reach the “herd immunity” threshold needed to stop transmission and achieve elimination.

scholarly journals Assessing the impact of preventive mass vaccination campaigns on yellow fever outbreaks in Africa : a population-level self-controlled case-series study

2020 ◽  
Author(s):  
Kevin Jean ◽  
Hanaya Raad ◽  
Katy A. M. Gaythorpe ◽  
Arran Hamlet ◽  
Judith E. Mueller ◽  
...  
Keyword(s):  
Yellow Fever ◽  
Case Series ◽  
Public Health Intervention ◽  
Population Level ◽  
Mass Vaccination ◽  
Sensitivity Analyses ◽  
Endemic Region ◽  
Case Series Study ◽  
Vaccination Campaigns ◽  
The Impact

Introduction: The Eliminate Yellow fever Epidemics (EYE) strategy was launched in 2017 in response to the resurgence of yellow fever in Africa and the Americas. The strategy relies on several vaccination activities, including preventive mass vaccination campaigns (PMVCs). However, by how much PMVCs decrease the risk of outbreak to occur has not yet been quantified. Methods: We used the self-controlled case series (SCCS) method to assess the association between the occurrence of yellow fever outbreaks and the implementation of PMVCs at the province level in the African endemic region. As all time-invariant confounders are implicitly controlled for, the SCCS method is an alternative to classical cohort or case-control study designs when the risk of residual confounding is high. The location and dates of outbreaks were identified from international epidemiological records, and information on PMVCs was provided by coordinators of vaccination activities and international funders. The study sample consisted of provinces that were both affected by an outbreak and targeted for a PMVC between 2005 and 2018. We compared the relative incidence of outbreaks before and after the implementation of a PMVC. The sensitivity of our estimates to a range of assumptions was explored, and the results of the SCCS method were compared to those obtained through a retrospective cohort study design. We further derived the number of yellow fever outbreaks that have been prevented by PMVCs. Results: The study sample consisted of 33 African provinces. Among these, outbreaks occurred during the pre-PMVC period in 26 (78.8%) provinces versus 7 (21.2%) occurring in the post-PMVC period. This corresponded to a significantly reduced incidence rate ratio of 0.14 (95% Confidence interval 0.06 to 0.34) for the post-PMVC versus pre-PMVC period. This estimate was robust across a range of sensitivity analyses, while the results of the cohort-style analyses were highly sensitive to the choice of covariates included in the model. Based on the SCCS results, we estimated that PMVCs have reduced the number of outbreaks by 34% (22% to 45%) in Africa over the study period. Conclusion: Our estimates provide new empirical evidence of the high preventive impact of PMVCs on yellow fever outbreaks. This study illustrates that the SCCS method can be advantageously applied at the population level in order to evaluate a public health intervention.

scholarly journals Assessing the impact of preventive mass vaccination campaigns on yellow fever outbreaks in Africa: A population-level self-controlled case series study

PLoS Medicine ◽  
2021 ◽  
Vol 18 (2) ◽  
pp. e1003523
Author(s):  
Kévin Jean ◽  
Hanaya Raad ◽  
Katy A. M. Gaythorpe ◽  
Arran Hamlet ◽  
Judith E. Mueller ◽  
...  
Keyword(s):  
Yellow Fever ◽  
Case Series ◽  
Population Level ◽  
Mass Vaccination ◽  
Sensitivity Analyses ◽  
Environmental Drivers ◽  
Case Series Study ◽  
Vaccination Campaigns ◽  
The Impact ◽  
Province Level

Background The Eliminate Yellow fever Epidemics (EYE) strategy was launched in 2017 in response to the resurgence of yellow fever in Africa and the Americas. The strategy relies on several vaccination activities, including preventive mass vaccination campaigns (PMVCs). However, to what extent PMVCs are associated with a decreased risk of outbreak has not yet been quantified. Methods and findings We used the self-controlled case series (SCCS) method to assess the association between the occurrence of yellow fever outbreaks and the implementation of PMVCs at the province level in the African endemic region. As all time-invariant confounders are implicitly controlled for in the SCCS method, this method is an alternative to classical cohort or case–control study designs when the risk of residual confounding is high, in particular confounding by indication. The locations and dates of outbreaks were identified from international epidemiological records, and information on PMVCs was provided by coordinators of vaccination activities and international funders. The study sample consisted of provinces that were both affected by an outbreak and targeted for a PMVC between 2005 and 2018. We compared the incidence of outbreaks before and after the implementation of a PMVC. The sensitivity of our estimates to a range of assumptions was explored, and the results of the SCCS method were compared to those obtained through a retrospective cohort study design. We further derived the number of yellow fever outbreaks that have been prevented by PMVCs. The study sample consisted of 33 provinces from 11 African countries. Among these, the first outbreak occurred during the pre-PMVC period in 26 (79%) provinces, and during the post-PMVC period in 7 (21%) provinces. At the province level, the post-PMVC period was associated with an 86% reduction (95% CI 66% to 94%, p < 0.001) in the risk of outbreak as compared to the pre-PMVC period. This negative association between exposure to PMVCs and outbreak was robustly observed across a range of sensitivity analyses, especially when using quantitative estimates of vaccination coverage as an alternative exposure measure, or when varying the observation period. In contrast, the results of the cohort-style analyses were highly sensitive to the choice of covariates included in the model. Based on the SCCS results, we estimated that PMVCs were associated with a 34% (95% CI 22% to 45%) reduction in the number of outbreaks in Africa from 2005 to 2018. A limitation of our study is the fact that it does not account for potential time-varying confounders, such as changing environmental drivers of yellow fever and possibly improved disease surveillance. Conclusions In this study, we provide new empirical evidence of the high preventive impact of PMVCs on yellow fever outbreaks. This study illustrates that the SCCS method can be advantageously applied at the population level in order to evaluate a public health intervention.

scholarly journals A narrative review on HPV vaccination among boys and men

2020 ◽  
pp. 9-12
Author(s):  
Vinod K Ramani ◽  
Radheshyam Naik
Keyword(s):  
Hpv Vaccine ◽  
Hpv Vaccination ◽  
Herd Immunity ◽  
Population Level ◽  
Hpv Infection ◽  
Level Control ◽  
Anogenital Warts ◽  
Indian Context ◽  
Present Generation ◽  
The Cost

Apart from cervical cancer, Human papillomavirus (HPV) infection is associated with head and neck as well as other anogenital cancers such as vulva, vagina, anus, and penis. HPV vaccine provides specific protection against the disease and its subsequent manifestations.Vaccination programs for men tend to improve population-level control of HPV infection and directly prevent HPV related disease such as anogenital warts and oropharyngeal cancers in males. HPV vaccine does not treat existing infection or lesions/cancer and is intended for individuals before initiation fo sexual activity or any other form of exposure to HPV.Many programs across the globe do not include vaccination for boys because of the cost and little recognition of the emerging epidemic of HPV associated cancers in men. In the Indian context, as screening is not feasible for non-cervical HPV associated cancers, its incidence mostly among men will continue to rise until the present generation of vaccinated adolescents reaches their middle-age.Vaccination will reduce transmission rates and increase herd immunity. This in-turn, will prevent not just cervical cancers but also other HPV-associated malignancies among men and women.

scholarly journals Epidemiological Impact of SARS-CoV-2 Vaccination: Mathematical Modeling Analyses

Vaccines ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 668 ◽  
Author(s):  
Monia Makhoul ◽  
Houssein H. Ayoub ◽  
Hiam Chemaitelly ◽  
Shaheen Seedat ◽  
Ghina R. Mumtaz ◽  
...  
Keyword(s):  
Mathematical Modeling ◽  
Vaccine Development ◽  
Severe Disease ◽  
Herd Immunity ◽  
Social Contact ◽  
Population Level ◽  
Contact Rate ◽  
Disease Case ◽  
Major Outbreak ◽  
Vaccine Impact

This study aims to inform SARS-CoV-2 vaccine development/licensure/decision-making/implementation, using mathematical modeling, by determining key preferred vaccine product characteristics and associated population-level impacts of a vaccine eliciting long-term protection. A prophylactic vaccine with efficacy against acquisition (VES) ≥70% can eliminate the infection. A vaccine with VES <70% may still control the infection if it reduces infectiousness or infection duration among those vaccinated who acquire the infection, if it is supplemented with <20% reduction in contact rate, or if it is complemented with herd-immunity. At VES of 50%, the number of vaccinated persons needed to avert one infection is 2.4, and the number is 25.5 to avert one severe disease case, 33.2 to avert one critical disease case, and 65.1 to avert one death. The probability of a major outbreak is zero at VES ≥70% regardless of the number of virus introductions. However, an increase in social contact rate among those vaccinated (behavior compensation) can undermine vaccine impact. In addition to the reduction in infection acquisition, developers should assess the natural history and disease progression outcomes when evaluating vaccine impact.

Kinetics and Mechanism of Ecochemical Processes

2020 ◽  
pp. 109-136
Author(s):  
Sergey Olegovich Travin
Keyword(s):  
Mathematical Modeling ◽  
Numerical Experiment ◽  
Food Chain ◽  
Exponential Growth ◽  
Natural Waters ◽  
Stationary States ◽  
The Cost ◽  
Physical And Chemical ◽  
The Impact

Significant efforts of mankind and huge funds were spent to study the mechanisms of environmental processes. Recent decades have been marked by exponential growth of computer power and the accompanying decrease in the cost of computing. With regard to the mathematical modeling of physical and chemical processes that determine the quality of natural waters, atmosphere, and soil, this has led to the development of an extensive approach based on an increase in the number of components and reactions between them taken into consideration. In this chapter, the authors describe features of ecochemical systems and discuss the moments that complicates their prediction. Using the method of numerical experiment, they investigate the behavior of periodic systems with multiple stationary states. One conclusion is that the actual manifestation cannot be used to determine at what stage the impact occurred and to what stage of the food chain it relates. Another conclusion is that systems involving multiple stationary states are prone to bifurcations and chaotic jumps from one limit cycle to another.

scholarly journals Vaccination is Australia's most important COVID-19 public health action, even though herd immunity is unlikely

2021 ◽  
Author(s):  
Emma S McBryde ◽  
Michael T Meehan ◽  
Jamie Sziklay ◽  
Adeshina Adekunle ◽  
Abdul Kuddus ◽  
...  
Keyword(s):  
Reproduction Number ◽  
Control Strategies ◽  
Severe Disease ◽  
Herd Immunity ◽  
Public Health Action ◽  
Herd Protection ◽  
Health Action ◽  
The Impact ◽  
Indirect Protection ◽  
Better Than

The Australian National Cabinet four-step plan to transition to post-pandemic re-opening begins with vaccination to achieve herd protection and protection of the health system against a surge in COVID-19 cases. Assuming a pre-vaccination reproduction number for the Delta variant of 5, we show that for the current Mixed program of vaccinating over 60s with AstraZeneca and 16-60s with Pfizer we would not achieve herd immunity. We would need to cover 85% of the population (including many 5-16 year-olds to achieve herd immunity). At lower reproduction number of 3 and our current Mixed strategy, we can achieve herd immunity without vaccinating 5-15 year olds. This will be achieved at a 60% coverage pursuing a strategy targetting high transmitters or 70% coverage using a strategy targetting the vulnerable first. A reproduction number of 7 precludes achieving herd immunity, however vaccination is able to prevent 75% of deaths compared with no vaccination. We also examine the impact of vaccination on death in the event that herd immunity is not achieved. Direct effects of vaccination on reducing death are very good for both Pfizer and AstraZeneca vaccines. However we estimate that the Mixed or Pfizer program performs better than the AstraZeneca program. Furthermore, vaccination levels below the herd immunity threshold can lead to substantial (albeit incomplete) indirect protection for both vaccinated and unvaccinated populations. Given the potential for not reaching herd immunity, we need to consider what level of severe disease and death is acceptable, balanced against the consequences of ongoing aggressive control strategies.

Relaxing Synchronization Constraints in Distributed Agent-based Simulations

2013 ◽  
Vol 63 (3) ◽  
Author(s):  
Omar Rihawi ◽  
Yann Secq ◽  
Philippe Mathieu
Keyword(s):  
Time Management ◽  
Large Scale ◽  
Computer Network ◽  
Population Level ◽  
Emergent Properties ◽  
Agent Based ◽  
Multi Agent ◽  
The Cost ◽  
The Impact ◽  
Synchronization Constraints

In the context of situated agents simulations, when the number of agents increases, the number of their interactions will be increased too. These growths leads to higher requirements in memory and computation power. When simulations involve millions of agents, it becomes necessary to distribute the simulator on a computer network. In this paper we study the impact of synchronization policies in such context. Our claim is that when millions of agents are used in a simulation, because observations of these complex systems is made at the population level, emergent properties at the macroscopic level should not be highly impacted if some failure appears at the microscopic level. This paper is focused on the study of the impact of synchronization relaxation in the context of large scale situated agents simulations. We evaluate the cost in performance of several synchronization policies and their impact on the macroscopic properties of simulations. To that aims, we study three different time management mechanisms and evaluate them on two multi-agent applications.

scholarly journals Social Distancing, Lockdown and the Wide Use of Mask; A Magic Solution or a Double-Edged Sword for Respiratory Viruses Epidemiology?

Vaccines ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 595
Author(s):  
Ivan Sanz-Muñoz ◽  
Sonia Tamames-Gómez ◽  
Javier Castrodeza-Sanz ◽  
José María Eiros-Bouza ◽  
Raul Ortiz de Lejarazu-Leonardo
Keyword(s):  
Respiratory Syncytial Virus ◽  
Herd Immunity ◽  
Respiratory Viruses ◽  
Mass Vaccination ◽  
Influenza Vaccines ◽  
Social Distancing ◽  
Collateral Effects ◽  
Syncytial Virus ◽  
Vaccination Campaigns ◽  
Pharmaceutical Interventions

The use of non-pharmaceutical interventions (NPIs), such as social distancing, lockdowns and the massive use of masks, have not only largely prevented the spread of SARS-CoV-2, but also of other respiratory viruses such as influenza or respiratory syncytial virus (RSV). This decrease has been so high that, in most countries, the influenza and RSV epidemic has not occurred. Far from being a beneficial fact, this can be problematic, since the absence of circulation of certain pathogens can lead to a decrease in herd immunity against them. This can promote the rise of more serious, longer-lasting epidemics that start sooner. To alleviate the collateral effects that may occur due to the decrease in circulation of viruses such as influenza, it is necessary to increase the production of influenza vaccines, carry out mass vaccination campaigns and focus on vaccinating the main drivers of this virus, children.

scholarly journals Age-related changes in the rate of disease transmission: implications for the design of vaccination programmes

1985 ◽  
Vol 94 (3) ◽  
pp. 365-436 ◽  
Author(s):  
R. M. Anderson ◽  
R. M. May
Keyword(s):  
Disease Incidence ◽  
Temporal Trends ◽  
Herd Immunity ◽  
Mass Vaccination ◽  
Parameter Estimates ◽  
Age Dependency ◽  
Susceptibility To Infection ◽  
Age Related ◽  
The Impact ◽  
Apparent Age

SUMMARYMathematical models are developed to aid in the investigation of the implications of heterogeneity in contact with infection within a community, on the design of mass vaccination programmes for the control of childhood viral and bacterial infections in developed countries. Analyses are focused on age-dependency in the rate at which individuals acquire infection, the question of ‘who acquires infection from whom’, and the implications of genetic variability in susceptibility to infection. Throughout, theoretical predictions are based on parameter estimates obtained from epidemiological studies and are compared with observed temporal trends in disease incidence and age-stratified serological profiles.Analysis of case notification records and serological data suggest that the rate at which individuals acquire many common infections changes from medium to high and then to low levels in the infant, child and teenage plus adult age groups respectively. Such apparent age-dependency in attack rate acts to reduce slightly the predicted levels of herd immunity required for the eradication of infections such as measles, when compared with the predictions of models based on age-independent transmission. The action of maternally derived immunity in prohibiting vaccination in infants, and the broad span of age classes over which vaccination currently takes place in the U.K., however, argue that levels of herd immunity of between 90 and 94 % would be required to eliminate measles.Problems surrounding the interpretation of apparent age-related trends in the acquisition of infection and their relevance to the design of vaccination programmes, are discussed in relation to the possible role of genetically based variation in susceptibility to infection and observations on epidemics in “virgin” populations. Heterogeneous mixing models provide predictions of changes in serology and disease incidence under the impact of mass vaccination which well mirror observed trends in England and Wales.

scholarly journals The impact of protein-conjugate polysaccharide vaccines: an endgame for meningitis?

2013 ◽  
Vol 368 (1623) ◽  
pp. 20120147 ◽  
Author(s):  
Martin C. J. Maiden
Keyword(s):  
Herd Immunity ◽  
Age Groups ◽  
Population Level ◽  
Bacterial Diseases ◽  
Beneficial Effects ◽  
Health Innovations ◽  
Childhood Morbidity ◽  
Encapsulated Bacteria ◽  
Effective Public Health ◽  
The Impact

The development and implementation of conjugate polysaccharide vaccines against invasive bacterial diseases, specifically those caused by the encapsulated bacteria Neisseria meningitidis , Haemophilus influenzae and Streptococcus pneumoniae , has been one of the most effective public health innovations of the last 25 years. These vaccines have resulted in significant reductions in childhood morbidity and mortality worldwide, with their effectiveness due in large part to their ability to induce long-lasting immunity in a range of age groups. At the population level this immunity reduces carriage and interrupts transmission resulting in herd immunity; however, these beneficial effects can be counterbalanced by the selection pressures that immunity against carriage can impose, potentially promoting the emergence and spread of virulent vaccine escape variants. Studies following the implementation of meningococcal serogroup C vaccines improved our understanding of these effects in relation to the biology of accidental pathogens such as the meningococcus. This understanding has enabled the refinement of the implementation of conjugate polysaccharide vaccines against meningitis-associated bacteria, and will be crucial in maintaining and improving vaccine control of these infections. To date there is little evidence for the spread of virulent vaccine escape variants of the meningococcus and H. influenzae , although this has been reported in pneumococci.

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