COVID-19: did the masks work?

During the early stages of the COVID-19 pandemic, we called for mandatory public masking to 'flatten the curve'. We helped formulate a national standard (SWiFT 19) for barrier facemasks, and, using a novel laser-based approach, we determined that mask efficacy is dependent on both fabric and fit; with both variables being inversely related. Herein, we take a retrospective view of the role of masks during the pandemic and surmise that, on the balance of evidence to date, masks were effective at stemming the spread of SARS-CoV-2 and may well be an effective early control strategy for potential future respiratory pandemics.