Covid-19 sick days were 20 per cent lower in schools with air-cleaning HEPA filter machines, researchers on an eagerly-awaited study have found. But why has it taken so long to discover how well they work, asks Clare Wilson
Covid-19 sick days were 20 per cent lower in schools with air-cleaning HEPA filter machines, researchers on an eagerly-awaited study have found. But why has it taken so long to discover how well they work, asks Clare Wilson Covid-19 sick days were 20 per cent lower in schools with air-cleaning HEPA filter machines, researchers on an eagerly-awaited study have found. But why has it taken so long to discover how well they work, asks Clare Wilson