A 2021 paper reviewing worldwide mask use in 2020 summed up the potential benefits: “Reducing disease spread requires two things: limiting contacts of infected individuals via physical distancing and other measures and reducing the transmission probability per contact. The preponderance of evidence indicates that mask wearing reduces transmissibility per contact by reducing transmission of infected respiratory particles in both laboratory and clinical contexts.”
The same paper concludes:
“The available evidence suggests that near-universal adoption of nonmedical masks when out in public, in combination with complementary public health measures, could successfully reduce the effective reproduction rate to below 1, thereby reducing community spread if such measures are sustained.”
Those findings were in the context of earlier variants. As with most things, Omicron appears to be changing the game with masking rules. The CDC advises that masks are critical for preventing the spread of Omicron, but the type of mask has become more critical due to the nature of Omicron. Low quality masks unlikely to make much difference to the transmission of the virus. The Government has already recognised this by requiring, in the Prime Minister’s words, “an actual mask”.
Well-worn and high quality masks can help prevent spread, however there are currently no studies of mask effectiveness against community spread of Omicron that are equivalent to the review quoted above.
We can only conclude that mask wearing likely has significant benefits for reducing the spread of Omicron, although this is sensitive to mask quality.