Determining the optimal strategy for reopening schools, the impact of test and trace interventions, and the risk of occurrence of a second COVID-19 epidemic wave in the UK: a modelling study

Abstract

Summary Background As lockdown measures to slow the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection begin to ease in the UK, it is important to assess the impact of any changes in policy, including school reopening and broader relaxation of physical distancing measures. We aimed to use an individual-based model to predict the impact of two possible strategies for reopening schools to all students in the UK from September, 2020, in combination with different assumptions about relaxation of physical distancing measures and the scale-up of testing. Methods In this modelling study, we used Covasim, a stochastic individual-based model for transmission of SARS-CoV-2, calibrated to the UK epidemic. The model describes individuals' contact networks stratified into household, school, workplace, and community layers, and uses demographic and epidemiological data from the UK. We simulated six different scenarios, representing the combination of two school reopening strategies (full time and a part-time rota system with 50% of students attending school on alternate weeks) and three testing scenarios (68% contact tracing with no scale-up in testing, 68% contact tracing with sufficient testing to avoid a second COVID-19 wave, and 40% contact tracing with sufficient testing to avoid a second COVID-19 wave). We estimated the number of new infections, cases, and deaths, as well as the effective reproduction number (R) under different strategies. In a sensitivity analysis to account for uncertainties within the stochastic simulation, we also simulated infectiousness of children and young adults aged younger than 20 years at 50% relative to older ages (20 years and older). Findings With increased levels of testing (between 59% and 87% of symptomatic people tested at some point during an active SARS-CoV-2 infection, depending on the scenario), and effective contact tracing and isolation, an epidemic rebound might be prevented. Assuming 68% of contacts could be traced, we estimate that 75% of individuals with symptomatic infection would need to be tested and positive cases isolated if schools return full-time in September, or 65% if a part-time rota system were used. If only 40% of contacts could be traced, these figures would increase to 87% and 75%, respectively. However, without these levels of testing and contact tracing, reopening of schools together with gradual relaxing of the lockdown measures are likely to induce a second wave that would peak in December, 2020, if schools open full-time in September, and in February, 2021, if a part-time rota system were adopted. In either case, the second wave would result in R rising above 1 and a resulting second wave of infections 2·0–2·3 times the size of the original COVID-19 wave. When infectiousness of children and young adults was varied from 100% to 50% of that of older ages, we still found that a comprehensive and effective test–trace–isolate strategy would be r...

The potential contribution of face coverings to the control of SARS-CoV-2 transmission in schools and broader society in the UK: a modelling study

“…Transmission model Analogous to our recently published work [28], we modelled the spread of COVID-19 using Covasim, a stochastic individual-based model of SARS-CoV-2 transmission across a population. Development and implementation details can be found at http://docs.covasim.org with the methodology outlined in [36].…”

“…Development and implementation details can be found at http://docs.covasim.org with the methodology outlined in [36]. The model was previously applied to explore different scenarios of schools reopening in the UK [28], explore the epidemic spread in Australia [37] and explore different non-pharmaceutical interventions for epidemic control in Seattle, USA [36]. The code used to run all simulations contained in this paper is available from https://github.com/Jasminapg/Covid-19-Analysis.…”

“…However, the magnitude of the effect of compulsory masking on COVID-19 incidence is still highly uncertain since there is no straightforward way to infer a change in transmission probability from a change in viral emission. Mathematical modelling, having already played an important role in informing policy around the COVID-19 pandemic [24][25][26][27][28][29][30][31], can help to assess the likely impact of compulsory masking. While existing models have looked at the impact of different non-pharmaceutical interventions, these have been primarily focused on evaluating the impact of the lockdown [29][30] or exploring the efficacy of different test-traceisolate (TTI) strategies [26][27][28]31].…”

“…Our recent work [28], which used the detailed individual based model called Covasim [36], highlighted that adequate TTI is needed to prevent a secondary epidemic wave when broader society including schools reopen in the UK. Here, we extend this work by calibrating Covasim, illustrated in Figures 1A-B, to recent data, to August 28, 2020 rather than June 17, 2020 as in [28], taking in consideration the slower-than-anticipated reopening of society in the UK during July and August, and to explore whether extending mandatory mask use to secondary school students alongside its existing use in some community settings could contribute to reducing the risk of COVID-19 wave resurgence later this year. The most recent findings from the CoMIX studies suggest that the contact rate in England is increasing much slower than anticipated with an average of 4 contacts per person during July and August compared to around 11 contacts per day in pre-COVID-19 era (personal communication with authors of [30] and based on unpublished follow on work from [30]).…”

Covid-19: NHS Test and Trace must improve for schools to reopen safely, say researchers

“…If schools reopened on a part time rota basis, this peak is likely to be in February 2021. In both cases the second wave of infections could be between 2 and 2.3 times the size of the original covid-19 wave, say the authors of the study, published in Lancet Child & Adolescent Health 1…”