evidence: Do mask mandates work? There is evidence that mask mandates can help curb transmission. Recently, Rebecca Nugent, a data scientist at Carnegie Mellon who has been tracking the impact of COVID-19 mitigation policies, looked at how the delta variant spread through the summer and fall. [...] "While having a mask mandate doesn't necessarily cease the spread, you can see a difference between ones that have kept a statewide mask mandate on and ones that haven't," she explains. She and her collaborators are still in the process of analyzing how big of a difference mask mandates make on case numbers.