Millions of children have started to return to school across Britain with new air and virus testing regimes aimed at preventing an explosion of cases among the least vaccinated section of the population. The UK government will spend £25 million ($34.5m) supplying 300,0000 carbon dioxide monitors in England from this month to assess the air circulating in classrooms as part of an attempt to understand and limit classroom infections. A similar measure has been announced in Wales after a surge in Covid-19 cases in Scotland, where pupils have already returned to the classroom. “We expect most schools to have exceptionally good ventilation,” UK Education Secretary Gavin Williamson said on Thursday. He declined to say how many monitors had been delivered and did not exclude the possibility of some lessons and assemblies taking place outside during colder months in the event of coronavirus outbreaks in schools. “It’s not something we would be expected to see an awful lot, especially in the autumn and winter,” he told the BBC. Teaching organisations said many schools were unlikely to see the testing devices until the end of October. Some schools complained that they had classrooms where windows could not be opened. Geoff Barton, head of the Association of School and College Leaders, said the devices merely detected whether there was a ventilation problem and did nothing to solve it. “In truth, this equipment should have been in place ready for the start of the autumn term, and arguably a lot earlier in the crisis, but it is a case of better late than never,” he said. Researcher Dr Rajesh Bhagat, of the University of Cambridge, said on Thursday that scientific studies showed that poor indoor air quality affected learning. The outbreak of the viral respiratory disease SARs in China in 2003 highlighted the issue of indoor transmission but countries have been slow to learn its lessons, said the researcher. Dr Bhagat said research had picked up in the past five years because of the growing awareness that indoor air quality was vital to health. Previous studies for the airline sector had revealed the importance of air filtration systems, which could be retrofitted in the worst-affected schools. The UK has also launched a trial of air purifiers in 30 schools in Bradford to see if they will reduce the risk of transmission. Dr Bhagat, who is currently involved in field studies in schools, was involved in a study by a team from Cambridge last year that found good ventilation and mask-wearing reduced the threat of transmission inside buildings. Wearing masks is not recommended under the current return-to-school measures. But the study suggested that efforts to reduce energy consumption and keep temperatures comfortable during a new era of climate change and global warming could be in conflict with efforts to prevent Covid-19 transmission. The pandemic has underscored the tension between energy efficiency and opening windows wide for good ventilation. “The CO2 sensors will give us some idea where it’s better or worse and where some interventions will be implemented in time,” he said. “The pandemic has shown one thing – that we know less than what we need to know to solve these problems.” The carbon dioxide monitors will allow schools to measure exhaled air and pinpoint where there are high levels of carbon dioxide concentration – and insufficient ventilation. Airflow relies on a complex combination of vents, windows and doors and the heat and movement produced by people inside the rooms. The monitors are only one solution being lined up by authorities in the UK to limit school-based infections. The Welsh government announced it would spend £3m on new ozone machines to disinfect classrooms but said it would look at early trials before going ahead. The return to schools after the summer break will be accompanied by a testing programme for pupils and staff. The main difference will be if a child tests positive for Covid-19, their classmates will not be sent home as a precaution. Schools and colleagues are being encouraged to increase hygiene and ventilation. Health officials are preparing to offer vaccines to all children aged 12 to 15 in England from this month if the move is approved by a scientific advisory group.