Does WHO recommend the use of masks with exhalation valves to prevent transmission of COVID-19?
No, WHO does not advise using masks or respirators with exhalation valves. These masks are intended for industrial workers to prevent dust and particles from being breathed in as the valve closes on inhale. However, the valve opens on exhale, making it easier to breathe but also allowing any virus to pass through the valve opening. This makes the mask ineffective at preventing the spread of COVID-19 or any other respiratory virus.
Coronavirus disease (COVID-19): Maskshttps://www.who.int/emergencies/diseases/novel-coronavirus-2019/question-and-answers-hub/q-a-detail/coronavirus-disease-covid-19-masks