The relative infectiousness of asymptomatic SARS-CoV-2 infected persons compared with symptomatic individuals: A rapid scoping review

Thompson

et al. 2021

Preprint

Background: Strategies involving rapid testing have been suggested as a way of reopening schools that minimises absences while controlling transmission. We assess the likely impact of rapid testing strategies using lateral flow tests (LFTs) on infections and absences in secondary schools, compared to a policy of isolating year group bubbles upon a pupil returning a positive polymerase chain reaction (PCR) test. Methods: We developed an individual-based model of a secondary school formed of exclusive year group bubbles (five year groups, with 200 pupils per year). By simulating infections over the course of a seven-week half-term, we compared the impact of differing strategies on transmission, absences, and testing volume. We also considered the sensitivity of results to underlying model assumptions. Findings: Repeated testing of year-group bubbles following case detection or regular mass-testing strategies result in a modest increase in infections compared to the policy of isolating year-group bubbles, but substantially reduce absences. When combined these two testing strategies can reduce infections to levels lower than would occur under year-group isolation, although such a policy requires a high volume of testing. Interpretation: Our results highlight the conflict between the goals of minimising within-school transmission, minimising absences and minimising testing burden. While mass and targeted testing strategies can reduce school transmission and absences, it may lead to a large number of daily tests.

Section: Methodsmentioning

confidence: 99%

Assessing the impact of secondary school reopening strategies on within-school COVID-19 transmission and absences: a modelling study

Leng

Thompson

et al. 2021

Preprint

“…The copyright holder for this this version posted October 18, 2020. ; https://doi.org/10.1101/2020.10.15.20208454 doi: medRxiv preprint REACT-1 study [25] Relative infectiousness of an asymptomatic Uniform(0.4,0.7) [26] would be released from isolation, as long as no other symptomatic cases (that are confirmed positive or awaiting test result) were present in the household. The index case remained in self-isolation if they had independently been identified via contact tracing as a contact of a known infected; otherwise, that student also left self-isolation.…”

Section: Testing and Isolation Measuresmentioning

confidence: 99%

“…There is currently limited data available to provide a robust quantitative estimate of the relative infectiousness of asymptomatic and symptomatic individuals infected with SARS-CoV-2, though there are some indications that asymptomatic individuals could be considered to be less infectious than symptomatic individuals [27,28]. Therefore, we set an asymptomatic individual to have a lower risk of transmitting infection compared to a symptomatic individual, with the current uncertainty reflected by sampling the value for the relative infectiousness of an asymptomatic in each simulation replicate from a Uniform(0.3,0.7) distribution.…”

Section: Asymptomatic Transmissionmentioning

confidence: 99%

Modelling SARS-CoV-2 transmission in a UK university setting

Atkins

Keeling

et al. 2020

Preprint

Background: Around 40% of school leavers in the UK attend university and individual universities generally host thousands of students each academic year. Bringing together these student communities during the COVID-19 pandemic may require strong interventions to control transmission. Prior modelling analysis of SARS-CoV-2 transmission within universities that use compartmental modelling approaches suggest that outbreaks are almost inevitable. Methods: We constructed a network-based model to capture the interactions of a student population in different settings (housing, social and study). For a single academic term of a representative campus-based university, we ran a susceptible-latent-infectious-recovered type epidemic process, parameterised according to available estimates for SARS-CoV-2. We investigated the impact of: adherence to (or effectiveness of) isolation and test and trace measures; single-room isolation of cases; supplementary mass testing. Results: Incorporating uncertainty in the asymptomatic fraction of cases and their associated infectivity, in the absence of interventions our model estimated that 16% (2% - 38%) of the student population could be infected during the autumn term. With full adherence to test, trace and isolate measures, we found lower cumulative infection estimates of 1.4% (0.4% - 5%). Irrespective of the adherence to isolation measures, on average a higher proportion of students resident on-campus became infected than off-campus. Room isolation generated minimal benefits. A one-off instance of mass testing would not drastically reduce the term-long case load or end-of-term prevalence, but regular weekly or fortnightly testing could reduce both measures by more than 50% (compared to having no mass testing). Conclusions: Our findings suggest SARS-CoV-2 may readily transmit in a university setting if there is limited adherence to nonpharmaceutical interventions and/or there are delays in receiving test results. Following isolation guidance and effective contact tracing curbed transmission and reduced the expected time an adhering student would spend in isolation. Additionally, widespread adherence throughout the term suppresses the amount of unwitting asymptomatic transmission to family and community members in the students' domicile regions at the end of term.

“…The copyright holder for this this version posted November 20, 2020. ; https://doi.org/10.1101/2020.11.18.20230649 doi: medRxiv preprint REACT-1 study [3,5] Relative infectiousness of an asymptomatic Uniform(0.3, 0.7) [28,29] negative probability of 0.13 [32]). On occasions where a negative result was given, household members would be released from isolation, as long as no other symptomatic cases (that are confirmed positive or awaiting test result) were present in the household.…”

Section: Testing and Isolation Measuresmentioning

confidence: 99%

“…Once isolation periods began they were seen out in full unless the test result was negative. We REACT-1 study [3,5] Relative infectiousness of an asymptomatic Uniform(0.3, 0.7) [28,29] assumed the test had 100% specificity and its sensitivity was dependent upon time since infection (we used a posterior median profile of the probability of detecting infection reported by Hellewell et al [32], obtained by fitting the model developed by Kucirka et al [33] combined with the SAFER study data [34]).…”

Section: Testing and Isolation Measuresmentioning

confidence: 99%

A network modelling approach to assess non-pharmaceutical disease controls in a worker population: An application to SARS-CoV-2

Atkins

Keeling

et al. 2020

Preprint

BackgroundAs part of a concerted pandemic response to protect public health, businesses can enact non-pharmaceutical controls to minimise exposure to pathogens in workplaces and premises open to the public. Amendments to working practices can lead to the amount, duration and/or proximity of interactions being changed, ultimately altering the dynamics of disease spread. These modifications could be specific to the type of business being operated.MethodsWe use a data-driven approach to parameterise an individual-based network model for transmission of SARS-CoV-2 amongst the working population, stratified into work sectors. The network is comprised of layered contacts to consider risk of spread in multiple encounter settings (workplaces, households, social and other). We analyse several interventions targeted towards working practices: mandating a fraction of the population to work from home, using temporally asynchronous work patterns and introducing measures to create ‘COVID-secure’ workplaces. We also assess the general role of adherence to (or effectiveness of) isolation and test and trace measures and demonstrate the impact of all these interventions across a variety of relevant metrics.ResultsThe progress of the epidemic can be significantly hindered by instructing a significant proportion of the workforce to work from home. Furthermore, if required to be present at the workplace, asynchronous work patterns can help to reduce infections when compared with scenarios where all workers work on the same days, particularly for longer working weeks. When assessing COVID-secure workplace measures, we found that smaller work teams and a greater reduction in transmission risk led to a flatter temporal profile for both infections and the number of people isolating, and reduced the probability of large, long outbreaks. Finally, following isolation guidance and engaging with contact tracing alone is an effective tool to curb transmission, but is highly sensitive to adherence levels.ConclusionsIn the absence of sufficient adherence to non-pharmaceutical interventions, our results indicate a high likelihood of SARS-CoV-2 spreading widely throughout a worker population. Given the heterogeneity of demographic attributes across worker roles, in addition to the individual nature of controls such as contact tracing, we demonstrate the utility of a network model approach to investigate workplace-targeted intervention strategies and the role of test, trace and isolation in tackling disease spread.