Scientists have called for a “traffic light” system to be used for schools to reopen more widely.

Professor Anthony Costello, professor of global health and sustainable development at UCL and a member of the Independent SAGE group of scientists, speaking at a meeting of the All-Party Parliamentary Group on Coronavirus yesterday, proposed the system, developed by his colleague Professor Karl Friston.

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Speaking about how it would be possible to reopen schools safely, Professor Costello said: “When you look at all of this, you have to ensure you’re keeping the R [Covid reproduction number] below 1 and stopping exponential growth, so you would want to open schools at a certain threshold level.

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“And my colleague Professor Karl Friston has quantified this as basically around 100 cases per 100,000 a day in your local area.

“If you get it below that then it’s safe to schools. And then you can categorise, as we have done, schools in low-incidence areas with less than 10 cases per 100,000, medium risk between 10 and 50 and higher risk areas, which would be greater than 50 or up to 100. Beyond 100 you wouldn’t open. And then we’ve got criteria about safety measures and the stringency of them you would impose.”

In an email to colleagues, Professor Friston said: “I think it is right that the particular ‘special measures’ for each traffic light level should be decided by headteachers - given the latitude they have to implement them.

“However, we can list the kinds of measures associated with each level of local risk for them to consider. We had previously considered lower-level local authorities to be the appropriate granularity for local decision-making.”

Independent SAGE has created a guide for headteachers to calculate the risks in their local area.

They would firstly identify the incidence of new cases per 100,000, using the UCL dashboard to do so.

For schools in low-incidence areas with fewer than 10 new cases per 100,000, schools could reopen to all pupils, using measures such as frequent handwashing, hourly ventilation and enhanced cleaning to prevent the spread of the coronavirus.

In high-incidence areas with new cases between 50 and 99 per 100,000, schools could use separate breaktimes, avoid group work, cancel physical education and employ daily spray cleaning.

The group advises that masks are worn in all secondary schools if they reopen more widely.

In his email to colleagues, Professor Friston added: “In terms of concrete recommendations, I don’t think it is useful to say things like, ‘Schools can reopen when infection rates are down to the levels at the end of last summer.’ It would be more useful to offer clear, quantitative and principled criteria - and a procedure for evaluating local risk.”