A novel approach for evaluating contact patterns and risk mitigation strategies for COVID-19 in English primary schools with application of structured expert judgement

Abstract

Personal contacts drive COVID-19 infections. After being closed (23 March 2020) UK primary schools partially re-opened on 1 June 2020 with social distancing and new risk mitigation strategies. We conducted a structured expert elicitation of teachers to quantify primary school contact patterns and how contact rates changed upon re-opening with risk mitigation measures in place. These rates, with uncertainties, were determined using a performance-based algorithm. We report mean number of contacts per day for four cohorts within schools, with associated 90% confidence ranges. Prior to lockdown, younger children (Reception and Year 1) made 15 contacts per day [range 8.35] within school, older children (Year 6) 18 contacts [range 5.55], teaching staff 25 contacts [range 4.55] and non-classroom staff 11 contacts [range 2.27]. After re-opening, the mean number of contacts was reduced by 53% for young children, 62% for older children, 60% for classroom staff and 64% for other staff. Contacts between teaching and non-teaching staff reduced by 80%. The distributions of contacts per person are asymmetric with heavy tail reflecting a few individuals with high contact numbers. Questions on risk mitigation and supplementary structured interviews elucidated how new measures reduced daily contacts in-school and contribute to infection risk reduction.

Pupils returning to primary schools in England during 2020: rapid estimations of punctual COVID-19 infection rates

“…For June 2020, we were unable to obtain detailed national figures for Cohorts 3 and 4 because DfE attendance information was not broken down into primary and secondary schools (and may have included some private sector schools). Instead, we drew on information from an elicitation of teachers in 36 primary schools in the Royal Society Schools network, described in a companion study [1]; key aspects of that elicitation study are reported in electronic supplementary material, Appendix A1. These elicited judgements projected an average 65% return of teachers and 58% return of other staff for early June 2020, noting considerable variations between individual schools.…”

“…By contrast, asymptomatic carriers may not be recognized at all. The in-school risk mitigation measures to reduce contacts between people, ensure hygiene and isolate persons who display possible COVID-19 symptoms [1] indicate they were effective in reducing opportunities for infection spread in June-July 2020.…”

Alternative Covid-19 mitigation measures in school classrooms: analysis using an agent-based model of SARS-CoV-2 transmission

“…Additionally, behavioural mitigation measures were instituted in March 2020 to reduce contacts within schools. To model the number of contacts, we use the results of a Structured Expert Judgement (SEJ) elicitation study [1] conducted in spring/summer 2020 in the UK. SEJ uses the collective knowledge of experts (here school teachers) to estimate quantities of interest and their uncertainties, and can be performed rapidly during crises to provide essential information to models and policy makers [11].…”

“…However, school managers are responsible for deciding whether to continue to 'bubble' classes to minimize interactions. Teachers and school leaders may also decide to continue to implement measures that reduce contacts within the classroom, so we adopt the two contact rates distributions from [1] that model contact rates for pre-Covid classrooms and reduced contact rates during the epidemic. Incidence rates are obtained from a national scale epidemiological model [15] with scenarios modelling a gradual or rapid return to pre-pandemic societal contact rates.…”

“…With our approach, sets of several classrooms collectively can be assessed as a way of quantifying transmission probabilities in individual schools. Statistical representation of close contacts, defined in [1] to be a face-to-face contact within 1 metre for at least 5 minutes, between children and adults within school settings is derived from a study of 36 primary schools in England using teachers' expert judgements, formally elicited in Spring/Summer 2020 [1]. That study included a comparison of anticipated contact rates in schools taking mitigation measures in the following September 2020, such as formation of bubbles, reduced class sizes and other social distancing rules, with previous, normal contact rates in 'pre-Covid' times.…”