A clutter of unhelpful pandemic rules is wearing people down. One-way systems in stores, outdoor mask mandates, ceaselessly cleaning groceries and packages – should these things be our top priorities for limiting the spread of COVID-19?

Harvard’s Joseph Allen is an associate professor of exposure assessment science and one of the world’s experts on why some indoor spaces are worse than others for spreading viruses. Like other experts, he agrees that poorly ventilated indoor sites are the prime spreading ground for SARS-CoV-2. So the longer people spend in any indoor space with other people, the greater the risk they pose to themselves and others.