Engagement and adherence trade-offs for SARS-CoV-2 contact tracing

Contact tracing is an important tool for allowing countries to ease lockdown policies introduced to combat SARS-CoV-2. For contact tracing to be effective, those with symptoms must self-report themselves while their contacts must self-isolate when asked. However, policies such as legal enforcement of self-isolation can create trade-offs by dissuading individuals from self-reporting. We use an existing branching process model to examine which aspects of contact tracing adherence should be prioritized. We consider an inverse relationship between self-isolation adherence and self-reporting engagement, assuming that increasingly strict self-isolation policies will result in fewer individuals self-reporting to the programme. We find that policies which increase the average duration of self-isolation, or that increase the probability that people self-isolate at all, at the expense of reduced self-reporting rate, will not decrease the risk of a large outbreak and may increase the risk, depending on the strength of the trade-off. These results suggest that policies to increase self-isolation adherence should be implemented carefully. Policies that increase self-isolation adherence at the cost of self-reporting rates should be avoided. This article is part of the theme issue ‘Modelling that shaped the early COVID-19 pandemic response in the UK’.

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A model of COVID-19 propagation based on a gamma subordinated negative binomial branching process

10.1101/2020.07.08.20149039 ◽

2020 ◽

Cited By ~ 1

Author(s):

Jérôme Levesque ◽

David W. Maybury ◽

R. H. A. David Shaw

Keyword(s):

Branching Process ◽

Negative Binomial ◽

Mitigation Strategies ◽

Contact Tracing ◽

Bayesian Hierarchical ◽

Disease Propagation ◽

Work Spaces ◽

Trade Offs ◽

Case Count ◽

Office Environments

AbstractWe build a parsimonious Crump-Mode-Jagers continuous time branching process of COVID-19 propagation based on a negative binomial process subordinated by a gamma subordinator. By focusing on the stochastic nature of the process in small populations, our model provides decision making insight into mitigation strategies as an outbreak begins. Our model accommodates contact tracing and isolation, allowing for comparisons between different types of intervention. We emphasize a physical interpretation of the disease propagation throughout which affords analytical results for comparison to simulations. Our model provides a basis for decision makers to understand the likely trade-offs and consequences between alternative outbreak mitigation strategies particularly in office environments and confined work-spaces. Combining the asymptotic limit of our model with Bayesian hierarchical techniques, we provide US county level inferences for the reproduction number from cumulative case count data over July and August of this year.

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Implication of backward contact tracing in the presence of overdispersed transmission in COVID-19 outbreaks

Wellcome Open Research ◽

10.12688/wellcomeopenres.16344.3 ◽

2021 ◽

Vol 5 ◽

pp. 239

Author(s):

Akira Endo ◽

Quentin J. Leclerc ◽

Gwenan M. Knight ◽

Graham F. Medley ◽

Katherine E. Atkins ◽

...

Keyword(s):

Process Model ◽

Branching Process ◽

Contact Tracing ◽

Level Variation ◽

Primary Case ◽

Typical Size ◽

Individual Level ◽

Outbreak Control ◽

Incremental Effectiveness ◽

Parameter Values

Introduction: Contact tracing has the potential to control outbreaks without the need for stringent physical distancing policies, e.g. civil lockdowns. Unlike forward contact tracing, backward contact tracing identifies the source of newly detected cases. This approach is particularly valuable when there is high individual-level variation in the number of secondary transmissions (overdispersion). Methods: By using a simple branching process model, we explored the potential of combining backward contact tracing with more conventional forward contact tracing for control of COVID-19. We estimated the typical size of clusters that can be reached by backward tracing and simulated the incremental effectiveness of combining backward tracing with conventional forward tracing. Results: Across ranges of parameter values consistent with dynamics of SARS-CoV-2, backward tracing is expected to identify a primary case generating 3-10 times more infections than a randomly chosen case, typically increasing the proportion of subsequent cases averted by a factor of 2-3. The estimated number of cases averted by backward tracing became greater with a higher degree of overdispersion. Conclusion: Backward contact tracing can be an effective tool for outbreak control, especially in the presence of overdispersion as is observed with SARS-CoV-2.

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Using a household-structured branching process to analyse contact tracing in the SARS-CoV-2 pandemic

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2020.0267 ◽

2021 ◽

Vol 376 (1829) ◽

pp. 20200267

Author(s):

Martyn Fyles ◽

Elizabeth Fearon ◽

Christopher Overton ◽

Tom Wingfield ◽

Graham F. Medley ◽

...

Keyword(s):

Process Model ◽

Branching Process ◽

Household Structure ◽

Contact Tracing ◽

Symptom Report ◽

Primary Model ◽

Imported Cases ◽

Strategic Implementation ◽

Household Members ◽

The Uk

We explore strategies of contact tracing, case isolation and quarantine of exposed contacts to control the SARS-CoV-2 epidemic using a branching process model with household structure. This structure reflects higher transmission risks among household members than among non-household members. We explore strategic implementation choices that make use of household structure, and investigate strategies including two-step tracing, backwards tracing, smartphone tracing and tracing upon symptom report rather than test results. The primary model outcome is the effect of contact tracing, in combination with different levels of physical distancing, on the growth rate of the epidemic. Furthermore, we investigate epidemic extinction times to indicate the time period over which interventions must be sustained. We consider effects of non-uptake of isolation/quarantine, non-adherence, and declining recall of contacts over time. Our results find that, compared to self-isolation of cases without contact tracing, a contact tracing strategy designed to take advantage of household structure allows for some relaxation of physical distancing measures but cannot completely control the epidemic absent of other measures. Even assuming no imported cases and sustainment of moderate physical distancing, testing and tracing efforts, the time to bring the epidemic to extinction could be in the order of months to years. This article is part of the theme issue ‘Modelling that shaped the early COVID-19 pandemic response in the UK’.

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The feasibility of targeted test-trace-isolate for the control of SARS-CoV-2 variants

F1000Research ◽

10.12688/f1000research.51164.1 ◽

2021 ◽

Vol 10 ◽

pp. 291

Author(s):

William Bradshaw ◽

Jonathan Huggins ◽

Alun Lloyd ◽

Kevin Esvelt

Keyword(s):

Process Model ◽

Branching Process ◽

Large Fraction ◽

Contact Tracing ◽

Rt Pcr ◽

Health Agencies ◽

The Common ◽

Ancestral Strain

The SARS-CoV-2 variant B.1.1.7 reportedly exhibits substantially higher transmission than the ancestral strain and may generate a major surge of cases before vaccines become widely available, while the P.1 and B.1.351 variants may be equally transmissible and also resist vaccines. All three variants can be sensitively detected by RT-PCR due to an otherwise rare del11288-11296 mutation in orf1ab; B.1.1.7 can also be detected using the common TaqPath kit. Testing, contact tracing, and isolation programs overwhelmed by SARS-CoV-2 could slow the spread of the new variants, which are still outnumbered by tracers in most countries. However, past failures and high rates of mistrust may lead health agencies to conclude that tracing is futile, dissuading them from redirecting existing tracers to focus on the new variants. Here we apply a branching-process model to estimate the effectiveness of implementing a variant-focused testing, contact tracing, and isolation strategy with realistic levels of performance. Our model indicates that bidirectional contact tracing can substantially slow the spread of SARS-CoV-2 variants even in regions where a large fraction of the population refuses to cooperate with contact tracers or to abide by quarantine and isolation requests.

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Using a household structured branching process to analyse contact tracing in the SARS-CoV-2 pandemic

10.1101/2021.02.03.21250992 ◽

2021 ◽

Author(s):

Martyn Fyles ◽

Elizabeth Fearon ◽

Christopher Overton ◽

Tom Wingfield ◽

Graham F Medley ◽

...

Keyword(s):

Process Model ◽

Branching Process ◽

Household Structure ◽

Contact Tracing ◽

Test Results ◽

Symptom Report ◽

Time Period ◽

Primary Model ◽

Imported Cases ◽

Household Members

AbstractWe explore strategies of contact tracing, case isolation and quarantine of exposed contacts to control the SARS-CoV-2 epidemic using a branching process model with household structure. This structure reflects higher transmission risks among household members than among non-household members, and is also the level at which physical distancing policies have been applied. We explore implementation choices that make use of household structure, and investigate strategies including two-step tracing, backwards tracing, smartphone tracing and tracing upon symptom report rather than test results. The primary model outcome is the effect on the growth rate of the epidemic under contact tracing in combination with different levels of physical distancing, and we investigate epidemic extinction times to indicate the time period over which interventions must be sustained. We consider effects of non-uptake of isolation/quarantine, non-adherence, and declining recall of contacts over time. We find that compared to self-isolation of cases but no contact tracing, a household-based contact tracing strategy allows for some relaxation of physical distancing measures; however, it is unable to completely control the epidemic in the absence of other measures. Even assuming no imported cases and sustainment of moderate distancing, testing and tracing efforts, the time to bring the epidemic to extinction could be in the order of months to years.

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The feasibility of targeted test-trace-isolate for the control of SARS-CoV-2 variants

10.1101/2021.01.11.21249612 ◽

2021 ◽

Author(s):

William J. Bradshaw ◽

Jonathan H. Huggins ◽

Alun L. Lloyd ◽

Kevin M. Esvelt

Keyword(s):

Process Model ◽

Branching Process ◽

Large Fraction ◽

Contact Tracing ◽

Rt Pcr ◽

Health Agencies ◽

The Common ◽

Ancestral Strain

AbstractThe SARS-CoV-2 variant B.1.1.7 reportedly exhibits substantially higher transmission than the ancestral strain and may generate a major surge of cases before vaccines become widely available, while the P.1 and B.1.351 variants may be equally transmissible and also resist vaccines. All three variants can be sensitively detected by RT-PCR due to an otherwise rare del11288-11296 mutation in orf1ab; B.1.1.7 can also be detected using the common TaqPath kit. Testing, contact tracing, and isolation programs overwhelmed by SARS-CoV-2 could slow the spread of the new variants, which are still outnumbered by tracers in most countries. However, past failures and high rates of mistrust may lead health agencies to conclude that tracing is futile, dissuading them from redirecting existing tracers to focus on the new variants. Here we apply a branching-process model to estimate the effectiveness of implementing a variant-focused testing, contact tracing, and isolation strategy with realistic levels of performance. Our model indicates that bidirectional contact tracing can substantially slow the spread of SARS-CoV-2 variants even in regions where a large fraction of the population refuses to cooperate with contact tracers or to abide by quarantine and isolation requests.

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Implication of backward contact tracing in the presence of overdispersed transmission in COVID-19 outbreaks

Wellcome Open Research ◽

10.12688/wellcomeopenres.16344.1 ◽

2020 ◽

Vol 5 ◽

pp. 239 ◽

Cited By ~ 3

Author(s):

Akira Endo ◽

Quentin J. Leclerc ◽

Gwenan M. Knight ◽

Graham F. Medley ◽

Katherine E. Atkins ◽

...

Keyword(s):

Process Model ◽

Branching Process ◽

Contact Tracing ◽

Level Variation ◽

Primary Case ◽

Typical Size ◽

Individual Level ◽

Outbreak Control ◽

Incremental Effectiveness ◽

Parameter Values

Introduction: Contact tracing has the potential to control outbreaks without the need for stringent physical distancing policies, e.g. civil lockdowns. Unlike forward contact tracing, backward contact tracing identifies the source of newly detected cases. This approach is particularly valuable when there is high individual-level variation in the number of secondary transmissions (overdispersion). Methods: By using a simple branching process model, we explored the potential of combining backward contact tracing with more conventional forward contact tracing for control of COVID-19. We estimated the typical size of clusters that can be reached by backward tracing and simulated the incremental effectiveness of combining backward tracing with conventional forward tracing. Results: Across ranges of parameter values consistent with dynamics of SARS-CoV-2, backward tracing is expected to identify a primary case generating 3-10 times more infections than average, typically increasing the proportion of subsequent cases averted by a factor of 2-3. The estimated number of cases averted by backward tracing became greater with a higher degree of overdispersion. Conclusion: Backward contact tracing can be an effective tool for outbreak control, especially in the presence of overdispersion as was observed with SARS-CoV-2.

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Implication of backward contact tracing in the presence of overdispersed transmission in COVID-19 outbreaks

Wellcome Open Research ◽

10.12688/wellcomeopenres.16344.2 ◽

2021 ◽

Vol 5 ◽

pp. 239 ◽

Cited By ~ 1

Author(s):

Akira Endo ◽

Quentin J. Leclerc ◽

Gwenan M. Knight ◽

Graham F. Medley ◽

Katherine E. Atkins ◽

...

Keyword(s):

Process Model ◽

Branching Process ◽

Contact Tracing ◽

Level Variation ◽

Primary Case ◽

Typical Size ◽

Individual Level ◽

Outbreak Control ◽

Incremental Effectiveness ◽

Parameter Values

Introduction: Contact tracing has the potential to control outbreaks without the need for stringent physical distancing policies, e.g. civil lockdowns. Unlike forward contact tracing, backward contact tracing identifies the source of newly detected cases. This approach is particularly valuable when there is high individual-level variation in the number of secondary transmissions (overdispersion). Methods: By using a simple branching process model, we explored the potential of combining backward contact tracing with more conventional forward contact tracing for control of COVID-19. We estimated the typical size of clusters that can be reached by backward tracing and simulated the incremental effectiveness of combining backward tracing with conventional forward tracing. Results: Across ranges of parameter values consistent with dynamics of SARS-CoV-2, backward tracing is expected to identify a primary case generating 3-10 times more infections than a randomly chosen case, typically increasing the proportion of subsequent cases averted by a factor of 2-3. The estimated number of cases averted by backward tracing became greater with a higher degree of overdispersion. Conclusion: Backward contact tracing can be an effective tool for outbreak control, especially in the presence of overdispersion as is observed with SARS-CoV-2.

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Digital Herd Immunity and COVID-19

10.1101/2020.04.15.20066720 ◽

2020 ◽

Cited By ~ 8

Author(s):

Vir B. Bulchandani ◽

Saumya Shivam ◽

Sanjay Moudgalya ◽

S. L. Sondhi

Keyword(s):

Phase Transition ◽

Process Model ◽

Branching Process ◽

Herd Immunity ◽

Contact Tracing ◽

Highly Efficient ◽

Traditional Notion ◽

Infected Population ◽

Disease Characteristics ◽

Promising Strategy

A population can be immune to epidemics even if not all of its individual members are immune to the disease, just as long as sufficiently many are immune—this is the traditional notion of herd immunity. In the smartphone era a population can be immune to epidemics even if not a single one of its members is immune to the disease—a notion we propose to call “digital herd immunity”, which is similarly an emergent characteristic of the population. This immunity arises because contact-tracing protocols based on smartphone capabilities can lead to highly efficient quarantining of infected population members and thus the extinguishing of nascent epidemics. When the disease characteristics are favorable and smartphone usage is high enough, the population is in this immune phase. As usage decreases there is a novel “contact tracing” phase transition to an epidemic phase. We present and study a simple branching-process model for COVID-19 and show that digital immunity is possible regardless of the proportion of non-symptomatic transmission. We believe this is a promising strategy for dealing with COVID-19 in many countries such as India, whose challenges of scale motivated us to undertake this study in the first place and whose case we discuss briefly.

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