| 1. |
- Favero, Martina, et al.
(författare)
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Modelling preventive measures and their effect on generation times in emerging epidemics
- 2022
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Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5689 .- 1742-5662. ; 19:191
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Tidskriftsartikel (refereegranskat)abstract
- We present a stochastic epidemic model to study the effect of various preventive measures, such as uniform reduction of contacts and transmission, vaccination, isolation, screening and contact tracing, on a disease outbreak in a homogeneously mixing community. The model is based on an infectivity process, which we define through stochastic contact and infectiousness processes, so that each individual has an independent infectivity profile. In particular, we monitor variations of the reproduction number and of the distribution of generation times. We show that some interventions, i.e. uniform reduction and vaccination, affect the former while leaving the latter unchanged, whereas other interventions, i.e. isolation, screening and contact tracing, affect both quantities. We provide a theoretical analysis of the variation of these quantities, and we show that, in practice, the variation of the generation time distribution can be significant and that it can cause biases in the estimation of reproduction numbers. The framework, because of its general nature, captures the properties of many infectious diseases, but particular emphasis is on COVID-19, for which numerical results are provided.
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| 2. |
- Marion, Glenn, et al.
(författare)
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Modelling : Understanding pandemics and how to control them
- 2022
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Ingår i: Epidemics. - : Elsevier BV. - 1755-4365 .- 1878-0067. ; 39
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Tidskriftsartikel (refereegranskat)abstract
- New disease challenges, societal demands and better or novel types of data, drive innovations in the structure, formulation and analysis of epidemic models. Innovations in modelling can lead to new insights into epidemic processes and better use of available data, yielding improved disease control and stimulating collection of better data and new data types. Here we identify key challenges for the structure, formulation, analysis and use of mathematical models of pathogen transmission relevant to current and future pandemics.
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| 3. |
- Thompson, Robin N., et al.
(författare)
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Key questions for modelling COVID-19 exit strategies
- 2020
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 287:1932
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Tidskriftsartikel (refereegranskat)abstract
- Combinations of intense non-pharmaceutical interventions (lockdowns) were introduced worldwide to reduce SARS-CoV-2 transmission. Many governments have begun to implement exit strategies that relax restrictions while attempting to control the risk of a surge in cases. Mathematical modelling has played a central role in guiding interventions, but the challenge of designing optimal exit strategies in the face of ongoing transmission is unprecedented. Here, we report discussions from the Isaac Newton Institute 'Models for an exit strategy' workshop (11-15 May 2020). A diverse community of modellers who are providing evidence to governments worldwide were asked to identify the main questions that, if answered, would allow for more accurate predictions of the effects of different exit strategies. Based on these questions, we propose a roadmap to facilitate the development of reliable models to guide exit strategies. This roadmap requires a global collaborative effort from the scientific community and policymakers, and has three parts: (i) improve estimation of key epidemiological parameters; (ii) understand sources of heterogeneity in populations; and (iii) focus on requirements for data collection, particularly in low-to-middle-income countries. This will provide important information for planning exit strategies that balance socio-economic benefits with public health.
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| 4. |
- Vegvari, Carolin, et al.
(författare)
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Commentary on the use of the reproduction number R during the COVID-19 pandemic
- 2022
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Ingår i: Statistical Methods in Medical Research. - : SAGE Publications. - 0962-2802 .- 1477-0334. ; 31:9, s. 1675-1685
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Tidskriftsartikel (refereegranskat)abstract
- Since the beginning of the COVID-19 pandemic, the reproduction number R has become a popular epidemiological metric used to communicate the state of the epidemic. At its most basic, R is defined as the average number of secondary infections caused by one primary infected individual. R seems convenient, because the epidemic is expanding if R>1 and contracting if R<1. The magnitude of R indicates by how much transmission needs to be reduced to control the epidemic. Using R in a naïve way can cause new problems. The reasons for this are threefold: (1) There is not just one definition of R but many, and the precise definition of R affects both its estimated value and how it should be interpreted. (2) Even with a particular clearly defined R, there may be different statistical methods used to estimate its value, and the choice of method will affect the estimate. (3) The availability and type of data used to estimate R vary, and it is not always clear what data should be included in the estimation. In this review, we discuss when R is useful, when it may be of use but needs to be interpreted with care, and when it may be an inappropriate indicator of the progress of the epidemic. We also argue that careful definition of R, and the data and methods used to estimate it, can make R a more useful metric for future management of the epidemic.
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| 5. |
- Widgren, Katarina, et al.
(författare)
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Modelling varicella vaccination - What does a lack of surge in herpes zoster incidence tell us about exogenous boosting?
- 2022
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Ingår i: Vaccine. - : Elsevier BV. - 0264-410X .- 1873-2518. ; 40:4, s. 673-681
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Tidskriftsartikel (refereegranskat)abstract
- Background: For decades, assessments of the impact of universal varicella vaccination on the epidemiology of varicella and herpes zoster (HZ) have been made using mathematical modelling. Decreased virus circulation and the resulting diminished exogenous boosting have been predicted to lead to a surge in HZ incidence. Lately, the exogenous boosting hypothesis has been challenged due to a lack of an extensive surge in HZ incidence in countries with, by now long-standing universal varicella vaccination.Methods: In a deterministic compartmental transmission model of varicella zoster virus disease, we model various levels and duration of protection from boosting to explore the impact of successful childhood varicella vaccination on HZ incidence.Results: Considering total HZ incidence, lifelong and strong protection from boosting give a stable incidence of HZ for about 60 years followed by a decline, whereas lifelong intermediate protection leads to a decline. So does weak protection of intermediate duration. Full and short protection, lead to a small surge, while full and intermediate protection lead to the largest HZ surge. HZ incidence by age group show that total incidence is the result of opposing increasing and decreasing trends in the various age groups over time.Conclusions: The absence of an extensive surge in HZ incidence after varicella vaccination can, especially during the first 20-30 years, occur in either strong, intermediate or weak boosting scenarios. The impact seems to depend on an interplay of the protective level and duration of the protection in determining the basic reactivation rate and the proportion of the population that is susceptible at the start of vaccination. However, the picture depends on whether the entire population or specific age groups are observed.
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