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

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.