Masks can stop 99.9% large COVID-19 droplets: Study Large COVID-19 droplets are main driver of virus transmission, while small ones may not necessarily reach another person due to their reduced size BusinessToday.In | December 24, 2020 | Updated 13:41 IST Mask can protect people from large coronavirus droplets even if they are standing only 50cm away from each other Face masks can reduce the risk of spreading large COVID-19 droplets by up to 99.9 per cent while speaking or coughing, a new study published in the journal Royal Society Open Science claims. The study was part of a lab experiment done using mechanical mannequins and human subjects.