Teaching unions, scientists, public health experts and parents are calling for masks to remain compulsory in classrooms in England to protect children and their families and reduce the risk of a third wave of Covid-19. In a letter to the education secretary, Gavin Williamson, the signatories claim current rates of vaccination are not yet sufficient to fully mitigate the impact of transmission among children on infection rates in the community. The government hopes to relax the requirement for pupils to wear face coverings in class at the next stage of the roadmap out of lockdown, due on 17 May. The letter also highlights growing concerns about the risks of developing long Covid after infection, warning that an estimated 43,000 children and 114,000 school staff are thought to be suffering from the condition, although the real figure could be far higher. Almost 20 leading scientists and public health experts from the universities of Oxford, Cambridge, Exeter and UCL, among others, have joined forces with five unions representing teachers and other school staff and parents to urge the government to keep the requirement for masks in place until at least 21 June. Last week the schools minister, Nick Gibb, told MPs on the cross-party Commons education committee that the government hoped to be able to lift the requirement, depending on scientific data. However, the letter warns: “To strip these necessary protections, when there are already too few mitigation measures in schools and when rates of Covid-19 are still significant, would have consequences for the health of our children and their parents as well as their communities.” It points out that after schools fully reopened in England on 8 March, the number of children testing positive for Covid-19 increased, so that by the start of the Easter break the prevalence of infection was higher in school-age children than in any other age group. Figures published by the Office for National Statistics on Tuesday show school infection rates down, with around 0.33% of pupils and 0.32% of staff in secondary schools testing positive for Covid-19 from mid to late March, compared with 1.22% and 1.64% in December. Meanwhile, the number of positive test results for primary schools was “too small” to include because of statistical disclosure criteria. Dr Deepti Gurdasani, a clinical epidemiologist and senior lecturer in machine learning at Queen Mary University of London, who is among the signatories to the letter, said: “We do not want a repeat of past mistakes that previously led to new waves, higher deaths, and prolonged lockdowns.” A Department for Education spokesperson said: “It is expected that face coverings will no longer be required in classrooms at step 3 of the roadmap, which will be no earlier than 17 May. The lifting of further restrictions at step 3 will follow a review of the latest data on infection and vaccination rates, and all other school safety measures, including regular asymptomatic testing, will remain in place.”