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

The current NHS Test and Trace programme in England must significantly improve if schools are to reopen safely in September and to avoid a second wave of covid-19, the authors of a new UK modelling study have warned.

The model suggests that reopening schools full time from September alongside relaxation of other social distancing measures, and without scaling up testing, will induce a second wave that would peak in December. 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

The researchers simulated scenarios with schools either reopening full time or on a part time rota system together with different testing scenarios. Assuming 68% of contacts could be traced, 75% of people with symptomatic infection would need to have covid-19 diagnosed and be isolated if schools returned full time in September, or 65% if a part time rota system were brought in. If only 40% of contacts could be traced, then 87% of infected individuals would need to be given a diagnosis and isolated, or 75% if schools returned part time.

However, if levels of diagnoses and contact tracing fall below this across the UK population, then reopening schools together with gradual relaxation of the lockdown measures would result in the reproduction number R rising above 1 and would lead to a second wave.

Study author Chris Bonell, professor of public health sociology at London School of Hygiene and Tropical Medicine, told a Science Media Centre briefing that currently only about 50% of contacts of people testing positive for coronavirus were being traced through the NHS Test and Trace system. He said that figures for the week to 22 July showed that 4242 people tested positive, of whom 81.4% were interviewed by contact tracers. Of those interviewed, 81.3% reported contacts, and of these contacts 75.1% were traced—giving an overall figure of around 50%. “It’s not good enough, basically,” he said.

The modelling assumed that reopening schools would allow 70% of parents to go back to work, with the remainder continuing to work from home. The model simulated increasing transmission of covid-19 not only in schools but also in workplaces and the community.

Russell Viner, professor of adolescent health at the UCL Great Ormond Street Institute of Child Health, told the briefing that schools could not be considered in isolation but were part of society. “We are not saying that opening schools will cause a second wave,” he said. “But if it is not done with sufficient mitigations then we will potentially face a significant second pandemic wave.”

Another assumption the modellers made was that asymptomatic infections account for 30% of onward transmitted infections. The model assumed that children were as infectious as adults, as the evidence that the level of infectiousness in children differed from that in adults is non-conclusive. However, the researchers re-ran the model with the assumption that children and teenagers were 50% as infectious as adults, and this made little difference to the results.

An observational study, also published in Lancet Child & Adolescent Health, found that the risk of children and staff transmitting covid-19 within Australian schools was very low when a good contact tracing system was in place.2 The study looked at real world data from 25 schools and nurseries in New South Wales between January and April. Although 12 children and 15 teachers went to school or nursery while infectious, only an additional 18 people later became infected, out of 1448 contacts (an attack rate of 1.2%).