Reopening schools fully in September without an effective test, trace and isolating strategy could result in a second wave of coronavirus more than twice the size of the first, according to a new modelling study.
Researchers from UCL and the London School of Hygiene and Tropical Medicine (LSHTM) examined the possible implications of schools reopening in the UK coupled with broader reopening of society, such as more parents returning to the workplace and increased socialising within the community.
The study, published in The Lancet Child and Adolescent Health, simulated what would happen in an "optimistic" scenario assuming 68% of contacts of people who tested positive could be traced.
In the more pessimistic scenario the system had 40% coverage.
The authors found that "with increased levels of testing… and effective contact tracing and isolation, an epidemic rebound might be prevented".
But in a worst-case scenario, a second wave could be 2.3 times higher than the first.
The model assumes that around 70% of people would return to workplaces once their children went back to school and up to a 90% increase of mixing within the community with schools reopening.
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One of the authors, Chris Bonell, professor of public health sociology at LSHTM, said the current testing system has "about 50% coverage".
"Our findings suggests that it might be possible [to avoid] a secondary epidemic wave in the UK, if enough people with symptomatic infection can be diagnosed and their contacts traced and effectively isolated," he said.
"Reopening schools fully in September, alongside reopening workplaces in society, without an effective test, trace, isolating (TTI) strategy could result in a second wave of infections between two and 2.3 times the size of the original wave.
"This is a scenario with model, not a prediction of what is going to happen. It all depends on the other measures and the level of TTI coverage.
"Currently, TTI is not achieving the levels that we modelled. Looking at the NHS reports from the TTI system, it looks like it's about 50% coverage."
He added: "The most recent data [shows] about 81% of positives are interviewed, about 81% of those report contacts and about 75% of those contacts are reached so overall that equates to coverage of 50%.
"It looks from the ONS data like there are about 4,200 new infections per day. And it looks like from the testing data there are about 4,200 testing positive per week. So it looks like about one in seven. So, that's not good enough, basically."
But he said the coverage rates were following an "upward trend".
The authors said that without appropriate 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".