From the Key Messages: " 'Masks are an essential part of our toolkit against COVID-19 [coronavirus disease 2019].' Face coverings reduce transmission by blocking the spray of droplets from talking, sneezing, coughing, singing, or shouting when worn over the mouth and nose.  'Vaccinations are vital, but they don't confer 100% immunity, meaning that masks are still a critical intervention to protect the unvaccinated -- and indeed the vaccinated -- from contracting and spreading COVID-19.' [...]  'Consistent mask-wearing is particularly key to reduce the spread of the virus among people who are asymptomatic or are yet to show symptoms.' [...]  'Taking several measures together often provides a result far greater than the sum of their parts.' This is the case with vaccines, masking, hand-washing, ventilation, and other interventions. All help reduce the spread and the severity of this pandemic, together they might actually stop it.  'Masks help reduce transmission which is key to reduce the risk of new variants.' [...]  'To be effective, face mask use must be widespread and consistent over time and across geographies;' [...]  'Face covering must not be perceived as a temporary measure but become a new social norm.' [...] [and 8] 'In order to achieve widespread understanding of the need for masking, consistent and clear public messaging on the importance of masking is vital to public adherence to mask wearing.' It is also key for general public trust in public health guidance and measures, including vaccines."
Pandemic Action Network
Pandemic Action Network: https://pandemicactionnetwork.org/